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cdc7253787
MyISAM and Aria used to lie to the server about the reflength value. One value was used internally, it was stored on disk, e.g. in indexes, and couldn't be changed without full table rebuild. A differently calculated value was reported to the server - that value was sometimes larger than the true reflength. That caused the server to allocate more memory per position than necessary - affecting filesort, join buffer usage, optimizer cost calculations, and may be more.
573 lines
21 KiB
Text
573 lines
21 KiB
Text
ALTER DATABASE test CHARACTER SET latin1 COLLATE latin1_swedish_ci;
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set optimizer_switch='mrr=on,mrr_sort_keys=on,index_condition_pushdown=on';
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set long_query_time=0.1;
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TEST GROUP 1:
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Typical cases of in-to-exists and materialization subquery strategies
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=====================================================================
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drop database if exists world;
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set names utf8;
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create database world character set latin1;
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use world;
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CREATE TABLE Country (
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Code char(3) NOT NULL default '',
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Name char(52) NOT NULL default '',
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SurfaceArea float(10,2) NOT NULL default '0.00',
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Population int(11) NOT NULL default '0',
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Capital int(11) default NULL,
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PRIMARY KEY (Code),
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UNIQUE INDEX (Name)
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);
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CREATE TABLE City (
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ID int(11) NOT NULL auto_increment,
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Name char(35) NOT NULL default '',
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Country char(3) NOT NULL default '',
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Population int(11) NOT NULL default '0',
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PRIMARY KEY (ID),
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INDEX (Population),
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INDEX (Country)
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);
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CREATE TABLE CountryLanguage (
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Country char(3) NOT NULL default '',
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Language char(30) NOT NULL default '',
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Percentage float(3,1) NOT NULL default '0.0',
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PRIMARY KEY (Country, Language),
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INDEX (Percentage)
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);
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Make the schema and data more diverse by adding more indexes, nullable
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columns, and NULL data.
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create index SurfaceArea on Country(SurfaceArea);
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create index Language on CountryLanguage(Language);
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create index CityName on City(Name);
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alter table City change population population int(11) null default 0;
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select max(id) from City into @max_city_id;
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insert into City values (@max_city_id + 1,'Kilifarevo','BGR',NULL);
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SELECT COUNT(*) FROM Country;
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COUNT(*)
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239
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SELECT COUNT(*) FROM City;
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COUNT(*)
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4080
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SELECT COUNT(*) FROM CountryLanguage;
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COUNT(*)
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984
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set @@optimizer_switch = 'in_to_exists=on,semijoin=on,materialization=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on';
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1. Subquery in a disjunctive WHERE clause of the outer query.
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Q1.1m:
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MATERIALIZATION: there are too many rows in the outer query
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to be looked up in the inner table.
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EXPLAIN
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SELECT count(*) FROM Country
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WHERE (Code IN (select Country from City where City.Population > 100000) OR
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Name LIKE 'L%') AND
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surfacearea > 100000;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY Country ALL Name,SurfaceArea NULL NULL NULL 239 Using where
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2 MATERIALIZED City ALL Population,Country NULL NULL NULL 4079 Using where
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SELECT count(*) FROM Country
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WHERE (Code IN (select Country from City where City.Population > 100000) OR
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Name LIKE 'L%') AND
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surfacearea > 100000;
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count(*)
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107
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Q1.1e:
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IN-EXISTS: the materialization cost is the same as above, but
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there are much fewer outer rows to be looked up, thus the
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materialization cost is too high to compensate for fast lookups.
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EXPLAIN
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SELECT Name FROM Country
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WHERE (Code IN (select Country from City where City.Population > 100000) OR
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Name LIKE 'L%') AND
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surfacearea > 10*1000000;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY Country range Name,SurfaceArea SurfaceArea 4 NULL 5 Using index condition; Using where; Rowid-ordered scan
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2 DEPENDENT SUBQUERY City index_subquery Population,Country Country 3 func 17 Using where
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SELECT Name FROM Country
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WHERE (Code IN (select Country from City where City.Population > 100000) OR
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Name LIKE 'L%') AND
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surfacearea > 10*1000000;
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Name
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Russian Federation
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Q1.2m:
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MATERIALIZATION: the IN predicate is pushed (attached) to the last table
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in the join order (Country, City), therefore there are too many row
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combinations to filter by re-executing the subquery for each combination.
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EXPLAIN
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SELECT *
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FROM Country, City
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WHERE City.Country = Country.Code AND
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Country.SurfaceArea < 3000 AND Country.SurfaceArea > 10 AND
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(City.Name IN
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(select Language from CountryLanguage where Percentage > 50) OR
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City.name LIKE '%Island%');
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY Country ALL PRIMARY,SurfaceArea NULL NULL NULL 239 Using where
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1 PRIMARY City ref Country Country 3 world.Country.Code 17 Using where
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2 MATERIALIZED CountryLanguage ALL Percentage,Language NULL NULL NULL 984 Using where
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EXPLAIN
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SELECT *
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FROM Country, City
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WHERE City.Country = Country.Code AND
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Country.SurfaceArea < 500 AND Country.SurfaceArea > 10 AND
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(City.Name IN
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(select Language from CountryLanguage where Percentage > 50) OR
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City.name LIKE '%Island%');
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY Country range PRIMARY,SurfaceArea SurfaceArea 4 NULL 32 Using index condition; Rowid-ordered scan
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1 PRIMARY City ref Country Country 3 world.Country.Code 17 Using where
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2 MATERIALIZED CountryLanguage ALL Percentage,Language NULL NULL NULL 984 Using where
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SELECT *
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FROM Country, City
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WHERE City.Country = Country.Code AND
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Country.SurfaceArea < 500 AND Country.SurfaceArea > 10 AND
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(City.Name IN
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(select Language from CountryLanguage where Percentage > 50) OR
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City.name LIKE '%Island%');
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Code Name SurfaceArea Population Capital ID Name Country population
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CCK Cocos (Keeling) Islands 14.00 600 2317 2317 West Island CCK 167
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Q1.2e:
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IN_EXISTS: join order is the same, but the left IN operand refers to
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only the first table in the join order (Country), so there are much
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fewer rows to filter by subquery re-execution.
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EXPLAIN
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SELECT *
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FROM Country, City
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WHERE City.Country = Country.Code AND
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Country.SurfaceArea < 3000 AND Country.SurfaceArea > 10 AND
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(Country.Name IN
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(select Language from CountryLanguage where Percentage > 50) OR
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Country.name LIKE '%Island%');
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY Country ALL PRIMARY,SurfaceArea NULL NULL NULL 239 Using where
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1 PRIMARY City ref Country Country 3 world.Country.Code 17
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2 DEPENDENT SUBQUERY CountryLanguage index_subquery Percentage,Language Language 30 func 2 Using where
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SELECT *
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FROM Country, City
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WHERE City.Country = Country.Code AND
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Country.SurfaceArea < 3000 AND Country.SurfaceArea > 10 AND
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(Country.Name IN
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(select Language from CountryLanguage where Percentage > 50) OR
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Country.name LIKE '%Island%');
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Code Name SurfaceArea Population Capital ID Name Country population
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VGB Virgin Islands, British 151.00 21000 537 537 Road Town VGB 8000
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CYM Cayman Islands 264.00 38000 553 553 George Town CYM 19600
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COK Cook Islands 236.00 20000 583 583 Avarua COK 11900
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FRO Faroe Islands 1399.00 43000 901 901 Tórshavn FRO 14542
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CXR Christmas Island 135.00 2500 1791 1791 Flying Fish Cove CXR 700
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KIR Kiribati 726.00 83000 2256 2255 Bikenibeu KIR 5055
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KIR Kiribati 726.00 83000 2256 2256 Bairiki KIR 2226
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CCK Cocos (Keeling) Islands 14.00 600 2317 2316 Bantam CCK 503
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CCK Cocos (Keeling) Islands 14.00 600 2317 2317 West Island CCK 167
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MHL Marshall Islands 181.00 64000 2507 2507 Dalap-Uliga-Darrit MHL 28000
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NRU Nauru 21.00 12000 2728 2727 Yangor NRU 4050
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NRU Nauru 21.00 12000 2728 2728 Yaren NRU 559
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NFK Norfolk Island 36.00 2000 2806 2806 Kingston NFK 800
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PLW Palau 459.00 19000 2881 2881 Koror PLW 12000
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MNP Northern Mariana Islands 464.00 78000 2913 2913 Garapan MNP 9200
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TCA Turks and Caicos Islands 430.00 17000 3423 3423 Cockburn Town TCA 4800
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TUV Tuvalu 26.00 12000 3424 3424 Funafuti TUV 4600
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VIR Virgin Islands, U.S. 347.00 93000 4067 4067 Charlotte Amalie VIR 13000
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Q1.3:
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For the same reasons as in Q2 IN-EXISTS and MATERIALIZATION chosen
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for each respective subquery.
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EXPLAIN
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SELECT City.Name, Country.Name
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FROM City,Country
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WHERE City.Country = Country.Code AND
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Country.SurfaceArea < 30000 AND Country.SurfaceArea > 10 AND
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((Country.Code, Country.Name) IN
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(select Country, Language from CountryLanguage where Percentage > 50) AND
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Country.Population > 3000000
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OR
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(Country.Code, City.Name) IN
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(select Country, Language from CountryLanguage));
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY Country ALL PRIMARY,SurfaceArea NULL NULL NULL 239 Using where
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1 PRIMARY City ref Country Country 3 world.Country.Code 17 Using where
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3 MATERIALIZED CountryLanguage index PRIMARY,Language PRIMARY 33 NULL 984 Using index
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2 DEPENDENT SUBQUERY CountryLanguage unique_subquery PRIMARY,Percentage,Language PRIMARY 33 func,func 1 Using where
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SELECT City.Name, Country.Name
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FROM City,Country
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WHERE City.Country = Country.Code AND
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Country.SurfaceArea < 30000 AND Country.SurfaceArea > 10 AND
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((Country.Code, Country.Name) IN
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(select Country, Language from CountryLanguage where Percentage > 50) AND
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Country.Population > 3000000
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OR
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(Country.Code, City.Name) IN
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(select Country, Language from CountryLanguage));
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Name Name
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Kigali Rwanda
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2. NOT IN subqueries
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Q2.1:
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Number of cities that are not capitals in countries with small population.
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MATERIALIZATION is 50 times faster because the cost of each subquery
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re-execution is much higher than the cost of index lookups into the
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materialized subquery.
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EXPLAIN
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select count(*) from City
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where City.id not in (select capital from Country
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where capital is not null and population < 100000);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY City index NULL PRIMARY 4 NULL 4079 Using where; Using index
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2 MATERIALIZED Country ALL NULL NULL NULL NULL 239 Using where
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Q2.2e:
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Countries that speak French, but do not speak English
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IN-EXISTS because the outer query filters many rows, thus
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there are few lookups to make.
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EXPLAIN
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SELECT Country.Name
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FROM Country, CountryLanguage
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WHERE Code NOT IN (SELECT Country FROM CountryLanguage WHERE Language = 'English')
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AND CountryLanguage.Language = 'French'
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AND Code = Country;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY CountryLanguage ref PRIMARY,Language Language 30 const 19 Using index condition
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1 PRIMARY Country eq_ref PRIMARY PRIMARY 3 world.CountryLanguage.Country 1 Using where
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2 DEPENDENT SUBQUERY CountryLanguage unique_subquery PRIMARY,Language PRIMARY 33 func,const 1 Using index; Using where
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SELECT Country.Name
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FROM Country, CountryLanguage
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WHERE Code NOT IN (SELECT Country FROM CountryLanguage WHERE Language = 'English')
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AND CountryLanguage.Language = 'French'
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AND Code = Country;
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Name
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France
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Saint Pierre and Miquelon
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Belgium
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Burundi
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Guadeloupe
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Haiti
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Madagascar
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Martinique
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Mayotte
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French Polynesia
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Rwanda
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Sao Tome and Principe
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Switzerland
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New Caledonia
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Lebanon
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Mauritius
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Andorra
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Italy
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Luxembourg
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Q2.2m:
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Countries that speak French OR Spanish, but do not speak English
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MATERIALIZATION because the outer query filters less rows than Q5-a,
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so there are more lookups.
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set statement optimizer_switch='rowid_filter=off' for
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EXPLAIN
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SELECT Country.Name
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FROM Country, CountryLanguage
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WHERE Code NOT IN (SELECT Country FROM CountryLanguage WHERE Language = 'English')
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AND (CountryLanguage.Language = 'French' OR CountryLanguage.Language = 'Spanish')
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AND Code = Country;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY CountryLanguage range PRIMARY,Language Language 30 NULL 44 Using index condition; Rowid-ordered scan
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1 PRIMARY Country eq_ref PRIMARY PRIMARY 3 world.CountryLanguage.Country 1 Using where
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3 DEPENDENT SUBQUERY CountryLanguage unique_subquery PRIMARY,Language PRIMARY 33 func,const 1 Using index; Using where
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set statement optimizer_switch='rowid_filter=off' for
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SELECT Country.Name
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FROM Country, CountryLanguage
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WHERE Code NOT IN (SELECT Country FROM CountryLanguage WHERE Language = 'English')
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AND (CountryLanguage.Language = 'French' OR CountryLanguage.Language = 'Spanish')
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AND Code = Country;
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Name
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Andorra
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Argentina
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Bolivia
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Chile
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Costa Rica
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Dominican Republic
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Ecuador
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El Salvador
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Spain
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Guatemala
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Honduras
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Colombia
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Cuba
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Mexico
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Nicaragua
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Panama
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Paraguay
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Peru
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France
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Saint Pierre and Miquelon
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Uruguay
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Venezuela
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Belgium
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Burundi
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Guadeloupe
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Haiti
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Madagascar
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Martinique
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Mayotte
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French Polynesia
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Rwanda
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Sao Tome and Principe
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Switzerland
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New Caledonia
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Lebanon
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Mauritius
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Andorra
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Italy
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Luxembourg
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France
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Sweden
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Q2.3e:
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Not a very meaningful query that tests NOT IN.
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IN-EXISTS because the outer query is cheap enough to reexecute many times.
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EXPLAIN
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select count(*)
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from CountryLanguage
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where (Language, Country) NOT IN
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(SELECT City.Name, Country.Code
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FROM City LEFT JOIN Country ON (Country = Code and City.Population < 10000))
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AND Language IN ('English','Spanish');
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY CountryLanguage range Language Language 30 NULL 73 Using index condition; Using where; Rowid-ordered scan
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2 DEPENDENT SUBQUERY City ref CityName CityName 35 func 1 Using index condition
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2 DEPENDENT SUBQUERY Country eq_ref PRIMARY PRIMARY 3 world.City.Country 1 Using where; Using index
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select count(*)
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from CountryLanguage
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where (Language, Country) NOT IN
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(SELECT City.Name, Country.Code
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FROM City LEFT JOIN Country ON (Country = Code and City.Population < 10000))
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AND Language IN ('English','Spanish');
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count(*)
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88
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Q2.3m:
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MATERIALIZATION with the PARTIAL_MATCH_MERGE strategy, because the HAVING
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clause prevents the use of the index on City(Name), and in practice reduces
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radically the size of the temp table.
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EXPLAIN
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select count(*)
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from CountryLanguage
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where (Language, Country) NOT IN
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(SELECT City.Name, Country.Code
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FROM City LEFT JOIN Country ON (Country = Code)
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HAVING City.Name LIKE "Santa%");
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY CountryLanguage index NULL PRIMARY 33 NULL 984 Using where; Using index
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2 MATERIALIZED City ALL NULL NULL NULL NULL 4079
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2 MATERIALIZED Country eq_ref PRIMARY PRIMARY 3 world.City.Country 1 Using index
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select count(*)
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from CountryLanguage
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where (Language, Country) NOT IN
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(SELECT City.Name, Country.Code
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FROM City LEFT JOIN Country ON (Country = Code)
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HAVING City.Name LIKE "Santa%");
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count(*)
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984
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3. Subqueries with GROUP BY, HAVING, and aggregate functions
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Q3.1:
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Languages that are spoken in countries with 10 or 11 languages
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MATERIALIZATION is about 100 times faster than IN-EXISTS.
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EXPLAIN
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select count(*)
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from CountryLanguage
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where
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(Country, 10) IN (SELECT Code, COUNT(*) FROM CountryLanguage, Country
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WHERE Code = Country GROUP BY Code)
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OR
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(Country, 11) IN (SELECT Code, COUNT(*) FROM CountryLanguage, Country
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WHERE Code = Country GROUP BY Code)
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order by Country;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY CountryLanguage index NULL PRIMARY 33 NULL 984 Using where; Using index
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3 MATERIALIZED Country index PRIMARY PRIMARY 3 NULL 239 Using index
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3 MATERIALIZED CountryLanguage ref PRIMARY PRIMARY 3 world.Country.Code 4 Using index
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2 MATERIALIZED Country index PRIMARY PRIMARY 3 NULL 239 Using index
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2 MATERIALIZED CountryLanguage ref PRIMARY PRIMARY 3 world.Country.Code 4 Using index
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select count(*)
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from CountryLanguage
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where
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(Country, 10) IN (SELECT Code, COUNT(*) FROM CountryLanguage, Country
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WHERE Code = Country GROUP BY Code)
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OR
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(Country, 11) IN (SELECT Code, COUNT(*) FROM CountryLanguage, Country
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WHERE Code = Country GROUP BY Code)
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order by Country;
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count(*)
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102
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Q3.2:
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Countries whose capital is a city name that names more than one
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cities.
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MATERIALIZATION because the cost of single subquery execution is
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close to that of materializing the subquery.
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EXPLAIN
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select * from Country, City
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where capital = id and
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(City.name in (SELECT name FROM City
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GROUP BY name HAVING Count(*) > 2) OR
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capital is null);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY Country ALL NULL NULL NULL NULL 239 Using where
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1 PRIMARY City eq_ref PRIMARY PRIMARY 4 world.Country.Capital 1 Using where
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2 MATERIALIZED City index NULL CityName 35 NULL 4079 Using index
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select * from Country, City
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where capital = id and
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(City.name in (SELECT name FROM City
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GROUP BY name HAVING Count(*) > 2) OR
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capital is null);
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Code Name SurfaceArea Population Capital ID Name Country population
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BMU Bermuda 53.00 65000 191 191 Hamilton BMU 1200
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BOL Bolivia 1098581.00 8329000 194 194 La Paz BOL 758141
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CRI Costa Rica 51100.00 4023000 584 584 San José CRI 339131
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HKG Hong Kong 1075.00 6782000 937 937 Victoria HKG 1312637
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SYC Seychelles 455.00 77000 3206 3206 Victoria SYC 41000
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Q3.3: MATERIALIZATION is 25 times faster than IN-EXISTS
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EXPLAIN
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SELECT Name
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FROM Country
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WHERE Country.Code NOT IN
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(SELECT Country FROM City GROUP BY Name HAVING COUNT(Name) = 1);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY Country ALL NULL NULL NULL NULL 239 Using where
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2 MATERIALIZED City ALL NULL NULL NULL NULL 4079 Using temporary
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SELECT Name
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FROM Country
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WHERE Country.Code NOT IN
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(SELECT Country FROM City GROUP BY Name HAVING COUNT(Name) = 1);
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Name
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Antigua and Barbuda
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Costa Rica
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Montserrat
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Norfolk Island
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Seychelles
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Antarctica
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Bouvet Island
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British Indian Ocean Territory
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South Georgia and the South Sandwich Islands
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Heard Island and McDonald Islands
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French Southern territories
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United States Minor Outlying Islands
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4. Subqueries in the SELECT and HAVING clauses
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Q4.1m:
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Capital information about very big cities
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MATERIALIZATION
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EXPLAIN
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select Name, City.id in (select capital from Country where capital is not null) as is_capital
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from City
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where City.population > 10000000;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY City range Population Population 5 NULL 3 Using index condition; Rowid-ordered scan
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2 MATERIALIZED Country ALL NULL NULL NULL NULL 239 Using where
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select Name, City.id in (select capital from Country where capital is not null) as is_capital
|
|
from City
|
|
where City.population > 10000000;
|
|
Name is_capital
|
|
Mumbai (Bombay) 0
|
|
Q4.1e:
|
|
IN-TO-EXISTS after adding an index to make the subquery re-execution
|
|
efficient.
|
|
create index CountryCapital on Country(capital);
|
|
EXPLAIN
|
|
select Name, City.id in (select capital from Country where capital is not null) as is_capital
|
|
from City
|
|
where City.population > 10000000;
|
|
id select_type table type possible_keys key key_len ref rows Extra
|
|
1 PRIMARY City range Population Population 5 NULL 3 Using index condition; Rowid-ordered scan
|
|
2 SUBQUERY Country index_subquery CountryCapital CountryCapital 5 func 2 Using index; Using where
|
|
select Name, City.id in (select capital from Country where capital is not null) as is_capital
|
|
from City
|
|
where City.population > 10000000;
|
|
Name is_capital
|
|
Mumbai (Bombay) 0
|
|
drop index CountryCapital on Country;
|
|
|
|
Q4.2:
|
|
MATERIALIZATION
|
|
EXPLAIN
|
|
SELECT City.Name, City.Population
|
|
FROM City JOIN Country ON City.Country = Country.Code
|
|
GROUP BY City.Name
|
|
HAVING City.Name IN (select Name from Country where population < 1000000);
|
|
id select_type table type possible_keys key key_len ref rows Extra
|
|
1 PRIMARY City ALL Country NULL NULL NULL 4079 Using temporary; Using filesort
|
|
1 PRIMARY Country eq_ref PRIMARY PRIMARY 3 world.City.Country 1 Using index
|
|
2 MATERIALIZED Country ALL Name NULL NULL NULL 239 Using where
|
|
Last_query_cost 5.934845
|
|
EXPLAIN
|
|
SELECT straight_join City.Name, City.Population
|
|
FROM Country JOIN City ON City.Country = Country.Code
|
|
GROUP BY City.Name
|
|
HAVING City.Name IN (select Name from Country where population < 1000000);
|
|
id select_type table type possible_keys key key_len ref rows Extra
|
|
1 PRIMARY Country index PRIMARY PRIMARY 3 NULL 239 Using index; Using temporary; Using filesort
|
|
1 PRIMARY City ref Country Country 3 world.Country.Code 17
|
|
2 MATERIALIZED Country ALL Name NULL NULL NULL 239 Using where
|
|
Last_query_cost 7.972473
|
|
EXPLAIN
|
|
SELECT City.Name, City.Population
|
|
FROM Country LEFT JOIN City ON City.Country = Country.Code
|
|
GROUP BY City.Name
|
|
HAVING City.Name IN (select Name from Country where population < 1000000);
|
|
id select_type table type possible_keys key key_len ref rows Extra
|
|
1 PRIMARY Country index NULL PRIMARY 3 NULL 239 Using index; Using temporary; Using filesort
|
|
1 PRIMARY City ref Country Country 3 world.Country.Code 17
|
|
2 MATERIALIZED Country ALL Name NULL NULL NULL 239 Using where
|
|
Last_query_cost 7.972473
|
|
SELECT City.Name, City.Population
|
|
FROM City JOIN Country ON City.Country = Country.Code
|
|
GROUP BY City.Name
|
|
HAVING City.Name IN (select Name from Country where population < 1000000);
|
|
Name Population
|
|
Djibouti 383000
|
|
Gibraltar 27025
|
|
Macao 437500
|
|
San Marino 2294
|
|
|
|
5. Subqueries with UNION
|
|
|
|
Q5.1:
|
|
EXPLAIN
|
|
SELECT * from City where (Name, 91) in
|
|
(SELECT Name, round(Population/1000)
|
|
FROM City
|
|
WHERE Country = "IND" AND Population > 2500000
|
|
UNION
|
|
SELECT Name, round(Population/1000)
|
|
FROM City
|
|
WHERE Country = "IND" AND Population < 100000);
|
|
id select_type table type possible_keys key key_len ref rows Extra
|
|
1 PRIMARY City ALL NULL NULL NULL NULL 4079 Using where
|
|
2 DEPENDENT SUBQUERY City ref Population,Country,CityName CityName 35 func 1 Using where
|
|
3 DEPENDENT UNION City ref Population,Country,CityName CityName 35 func 1 Using where
|
|
NULL UNION RESULT <union2,3> ALL NULL NULL NULL NULL NULL
|
|
SELECT * from City where (Name, 91) in
|
|
(SELECT Name, round(Population/1000)
|
|
FROM City
|
|
WHERE Country = "IND" AND Population > 2500000
|
|
UNION
|
|
SELECT Name, round(Population/1000)
|
|
FROM City
|
|
WHERE Country = "IND" AND Population < 100000);
|
|
ID Name Country population
|
|
1359 Hassan IND 90803
|
|
1360 Ambala Sadar IND 90712
|
|
1361 Baidyabati IND 90601
|
|
set @@optimizer_switch='default';
|
|
drop database world;
|
|
|
|
|
|
TEST GROUP 2:
|
|
Tests of various combinations of optimizer switches, types of queries,
|
|
available indexes, column nullability, constness of tables/predicates.
|
|
=====================================================================
|
|
set optimizer_switch=default;
|
|
ALTER DATABASE test CHARACTER SET utf8mb4 COLLATE utf8mb4_uca1400_ai_ci;
|