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operations) Before this change, the boolean predicates: - X IS TRUE, - X IS NOT TRUE, - X IS FALSE, - X IS NOT FALSE were implemented by expanding the Item tree in the parser, by using a construct like: Item_func_if(Item_func_ifnull(X, <value>), <value>, <value>) Each <value> was a constant integer, either 0 or 1. A bug in the implementation of the function IF(a, b, c), in Item_func_if::fix_length_and_dec(), would cause the following : When the arguments b and c are both unsigned, the result type of the function was signed, instead of unsigned. When the result of the if function is signed, space for the sign could be counted twice (in the max() expression for a signed argument, and in the total), causing the member max_length to be too high. An effect of this is that the final type of IF(x, int(1), int(1)) would be int(2) instead of int(1). With this fix, the problems found in Item_func_if::fix_length_and_dec() have been fixed. While it's semantically correct to represent 'X IS TRUE' with Item_func_if(Item_func_ifnull(X, <value>), <value>, <value>), there are however more problems with this construct. a) Building the parse tree involves : - creating 5 Item instances (3 ints, 1 ifnull, 1 if), - creating each Item calls my_pthread_getspecific_ptr() once in the operator new(size), and a second time in the Item::Item() constructor, resulting in a total of 10 calls to get the current thread. Evaluating the expression involves evaluating up to 4 nodes at runtime. This representation could be greatly simplified and improved. b) Transforming the parse tree internally with if(ifnull(...)) is fine as long as this transformation is internal to the server implementation. With views however, the result of the parse tree is later exposed by the ::print() functions, and stored as part of the view definition. Doing this has long term consequences: 1) The original semantic 'X IS TRUE' is lost, and replaced by the if(ifnull(...)) expression. As a result, SHOW CREATE VIEW does not restore the original code. 2) Should a future version of MySQL implement the SQL BOOLEAN data type for example, views created today using 'X IS NULL' can be exported using mysqldump, and imported again. Such views would be converted correctly and automatically to use a BOOLEAN column in the future version. With 'X IS TRUE' and the current implementations, views using these "boolean" predicates would not be converted during the export/import, and would use integer columns instead. The difference traces back to how SHOW CREATE VIEW preserves 'X IS NULL' but does not preserve the 'X IS TRUE' semantic. With this fix, internal representation of 'X IS TRUE' booleans predicates has changed, so that: - dedicated Item classes are created for each predicate, - only 1 Item is created to represent 1 predicate - my_pthread_getspecific_ptr() is invoked 1 time instead of 10 - SHOW CREATE VIEW preserves the original semantic, and prints 'X IS TRUE'. Note that, because of the fix in Item_func_if, views created before this fix will: - correctly use a int(1) type instead of int(2) for boolean predicates, - incorrectly print the if(ifnull(...), ...) expression in SHOW CREATE VIEW, since the original semantic (X IS TRUE) has been lost. - except for the syntax used in SHOW CREATE VIEW, these views will operate properly, no action is needed. Views created after this fix will operate correctly, and will preserve the original code semantic in SHOW CREATE VIEW. mysql-test/r/func_if.result: IF(x, unsigned, unsigned) should be unsigned. mysql-test/r/view.result: Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates. mysql-test/t/func_if.test: IF(x, unsigned, unsigned) should be unsigned. mysql-test/t/view.test: Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates. sql/item_cmpfunc.cc: Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates. IF(x, unsigned, unsigned) should be unsigned. sql/item_cmpfunc.h: Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates. sql/sql_yacc.yy: Preserve the semantic of 'X IS [NOT] (TRUE|FALSE)' boolean predicates.
133 lines
3.6 KiB
Text
133 lines
3.6 KiB
Text
drop table if exists t1;
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select IF(0,"ERROR","this"),IF(1,"is","ERROR"),IF(NULL,"ERROR","a"),IF(1,2,3)|0,IF(1,2.0,3.0)+0 ;
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IF(0,"ERROR","this") IF(1,"is","ERROR") IF(NULL,"ERROR","a") IF(1,2,3)|0 IF(1,2.0,3.0)+0
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this is a 2 2.0
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CREATE TABLE t1 (st varchar(255) NOT NULL, u int(11) NOT NULL) ENGINE=MyISAM;
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INSERT INTO t1 VALUES ('a',1),('A',1),('aa',1),('AA',1),('a',1),('aaa',0),('BBB',0);
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select if(1,st,st) s from t1 order by s;
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s
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a
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A
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a
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aa
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AA
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aaa
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BBB
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select if(u=1,st,st) s from t1 order by s;
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s
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a
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A
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a
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aa
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AA
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aaa
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BBB
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select if(u=1,binary st,st) s from t1 order by s;
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s
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A
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AA
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BBB
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a
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a
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aa
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aaa
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select if(u=1,st,binary st) s from t1 where st like "%a%" order by s;
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s
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A
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AA
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a
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a
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aa
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aaa
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explain extended select if(u=1,st,binary st) s from t1 where st like "%a%" order by s;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 ALL NULL NULL NULL NULL 7 Using where; Using filesort
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Warnings:
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Note 1003 select if((`test`.`t1`.`u` = 1),`test`.`t1`.`st`,cast(`test`.`t1`.`st` as char charset binary)) AS `s` from `test`.`t1` where (`test`.`t1`.`st` like _latin1'%a%') order by if((`test`.`t1`.`u` = 1),`test`.`t1`.`st`,cast(`test`.`t1`.`st` as char charset binary))
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select nullif(u, 1) from t1;
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nullif(u, 1)
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NULL
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NULL
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NULL
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NULL
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NULL
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0
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0
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explain extended select nullif(u, 1) from t1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 ALL NULL NULL NULL NULL 7
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Warnings:
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Note 1003 select nullif(`test`.`t1`.`u`,1) AS `nullif(u, 1)` from `test`.`t1`
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drop table t1;
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select nullif(1,'test');
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nullif(1,'test')
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1
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Warnings:
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Warning 1292 Truncated incorrect DOUBLE value: 'test'
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select NULLIF(NULL,NULL), NULLIF(NULL,1), NULLIF(NULL,1.0), NULLIF(NULL,"test");
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NULLIF(NULL,NULL) NULLIF(NULL,1) NULLIF(NULL,1.0) NULLIF(NULL,"test")
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NULL NULL NULL NULL
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select NULLIF(1,NULL), NULLIF(1.0, NULL), NULLIF("test", NULL);
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NULLIF(1,NULL) NULLIF(1.0, NULL) NULLIF("test", NULL)
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1 1.0 test
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create table t1 (num double(12,2));
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insert into t1 values (144.54);
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select sum(if(num is null,0.00,num)) from t1;
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sum(if(num is null,0.00,num))
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144.54
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drop table t1;
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create table t1 (x int, y int);
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insert into t1 values (0,6),(10,16),(20,26),(30,10),(40,46),(50,56);
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select min(if(y -x > 5,y,NULL)), max(if(y - x > 5,y,NULL)) from t1;
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min(if(y -x > 5,y,NULL)) max(if(y - x > 5,y,NULL))
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6 56
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drop table t1;
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create table t1 (a int);
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insert t1 values (1),(2);
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select if(1>2,a,avg(a)) from t1;
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if(1>2,a,avg(a))
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1.5000
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drop table t1;
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SELECT NULLIF(5,5) IS NULL, NULLIF(5,5) IS NOT NULL;
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NULLIF(5,5) IS NULL NULLIF(5,5) IS NOT NULL
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1 0
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CREATE TABLE `t1` (
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`id` int(11) NOT NULL ,
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`date` int(10) default NULL,
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`text` varchar(32) NOT NULL
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);
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INSERT INTO t1 VALUES (1,1110000000,'Day 1'),(2,1111000000,'Day 2'),(3,1112000000,'Day 3');
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SELECT id, IF(date IS NULL, '-', FROM_UNIXTIME(date, '%d-%m-%Y')) AS date_ord, text FROM t1 ORDER BY date_ord ASC;
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id date_ord text
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1 05-03-2005 Day 1
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2 16-03-2005 Day 2
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3 28-03-2005 Day 3
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SELECT id, IF(date IS NULL, '-', FROM_UNIXTIME(date, '%d-%m-%Y')) AS date_ord, text FROM t1 ORDER BY date_ord DESC;
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id date_ord text
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3 28-03-2005 Day 3
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2 16-03-2005 Day 2
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1 05-03-2005 Day 1
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DROP TABLE t1;
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CREATE TABLE t1 (a CHAR(10));
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INSERT INTO t1 VALUES ('aaa'), (NULL), (''), ('bbb');
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SELECT a, NULLIF(a,'') FROM t1;
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a NULLIF(a,'')
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aaa aaa
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NULL NULL
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NULL
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bbb bbb
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SELECT a, NULLIF(a,'') FROM t1 WHERE NULLIF(a,'') IS NULL;
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a NULLIF(a,'')
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NULL NULL
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NULL
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DROP TABLE t1;
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create table t1 (f1 int, f2 int);
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insert into t1 values(1,1),(0,0);
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select f1, f2, if(f1, 40.0, 5.00) from t1 group by f1 order by f2;
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f1 f2 if(f1, 40.0, 5.00)
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0 0 5.00
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1 1 40.00
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drop table t1;
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select if(0, 18446744073709551610, 18446744073709551610);
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if(0, 18446744073709551610, 18446744073709551610)
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18446744073709551610
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