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cdc9a1172d
Make SHOW EXPLAIN work for queries that do "Using temporary" and/or "Using filesort" - Patch#1: Don't lose "Using temporary/filesort" in the SHOW EXPLAIN output.
287 lines
10 KiB
Text
287 lines
10 KiB
Text
drop table if exists t0, t1, t2;
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create table t0 (a int);
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insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
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create table t1 (a int);
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insert into t1 select A.a + 10*B.a + 100*C.a from t0 A, t0 B, t0 C;
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alter table t1 add b int, add c int, add filler char(32);
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update t1 set b=a, c=a, filler='fooo';
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alter table t1 add key(a), add key(b);
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show explain for 2*1000*1000*1000;
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ERROR HY000: Unknown thread id: 2000000000
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show explain for (select max(a) from t0);
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ERROR 42000: This version of MySQL doesn't yet support 'Usage of subqueries or stored function calls as part of this statement'
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show explain for $thr2;
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ERROR HY000: Error when executing command SHOW EXPLAIN: Target is not running EXPLAINable command
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show explain for $thr1;
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ERROR HY000: Error when executing command SHOW EXPLAIN: Target is not running EXPLAINable command
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set @show_explain_probe_select_id=1;
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set debug='d,show_explain_probe_1';
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select count(*) from t1 where a < 100000;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 index a a 5 NULL 1000 Using where; Using index
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Warnings:
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Note 1003 select count(*) from t1 where a < 100000
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count(*)
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1000
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select max(c) from t1 where a < 10;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 range a a 5 NULL 10 Using index condition
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Warnings:
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Note 1003 select max(c) from t1 where a < 10
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max(c)
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9
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# We can catch EXPLAIN, too.
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set @show_expl_tmp= @@optimizer_switch;
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set optimizer_switch='index_condition_pushdown=on,mrr=on,mrr_sort_keys=on';
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explain select max(c) from t1 where a < 10;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 range a a 5 NULL 10 Using index condition; Rowid-ordered scan
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Warnings:
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Note 1003 explain select max(c) from t1 where a < 10
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 range a a 5 NULL 10 Using index condition; Rowid-ordered scan
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set optimizer_switch= @show_expl_tmp;
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# UNION, first branch
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set @show_explain_probe_select_id=1;
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set debug='d,show_explain_probe_1';
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explain select a from t0 A union select a+1 from t0 B;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY A ALL NULL NULL NULL NULL 10
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2 UNION B ALL NULL NULL NULL NULL 10
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NULL UNION RESULT <union1,2> ALL NULL NULL NULL NULL NULL
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Warnings:
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Note 1003 explain select a from t0 A union select a+1 from t0 B
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY A ALL NULL NULL NULL NULL 10
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2 UNION B ALL NULL NULL NULL NULL 10
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NULL UNION RESULT <union1,2> ALL NULL NULL NULL NULL NULL
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# UNION, second branch
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set @show_explain_probe_select_id=1;
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set debug='d,show_explain_probe_1';
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explain select a from t0 A union select a+1 from t0 B;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY A ALL NULL NULL NULL NULL 10
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2 UNION B ALL NULL NULL NULL NULL 10
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NULL UNION RESULT <union1,2> ALL NULL NULL NULL NULL NULL
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Warnings:
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Note 1003 explain select a from t0 A union select a+1 from t0 B
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY A ALL NULL NULL NULL NULL 10
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2 UNION B ALL NULL NULL NULL NULL 10
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NULL UNION RESULT <union1,2> ALL NULL NULL NULL NULL NULL
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# Uncorrelated subquery, select
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set @show_explain_probe_select_id=1;
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set debug='d,show_explain_probe_1';
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select a, (select max(a) from t0 B) from t0 A where a<1;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY A ALL NULL NULL NULL NULL 10 Using where
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2 SUBQUERY B ALL NULL NULL NULL NULL 10
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Warnings:
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Note 1003 select a, (select max(a) from t0 B) from t0 A where a<1
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a (select max(a) from t0 B)
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0 9
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# Uncorrelated subquery, explain
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set @show_explain_probe_select_id=1;
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set debug='d,show_explain_probe_1';
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explain select a, (select max(a) from t0 B) from t0 A where a<1;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY A ALL NULL NULL NULL NULL 10 Using where
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2 SUBQUERY B ALL NULL NULL NULL NULL 10
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Warnings:
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Note 1003 explain select a, (select max(a) from t0 B) from t0 A where a<1
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY A ALL NULL NULL NULL NULL 10 Using where
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2 SUBQUERY B ALL NULL NULL NULL NULL 10
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# correlated subquery, select
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set @show_explain_probe_select_id=1;
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set debug='d,show_explain_probe_1';
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select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY a ALL NULL NULL NULL NULL 10 Using where
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2 DEPENDENT SUBQUERY b ALL NULL NULL NULL NULL 10 Using where
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Warnings:
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Note 1003 select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
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a (select max(a) from t0 b where b.a+a.a<10)
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0 9
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# correlated subquery, explain
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set @show_explain_probe_select_id=1;
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set debug='d,show_explain_probe_1';
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select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY a ALL NULL NULL NULL NULL 10 Using where
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2 DEPENDENT SUBQUERY b ALL NULL NULL NULL NULL 10 Using where
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Warnings:
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Note 1003 select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
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a (select max(a) from t0 b where b.a+a.a<10)
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0 9
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# correlated subquery, select, while inside the subquery
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set @show_explain_probe_select_id=2;
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set debug='d,show_explain_probe_1';
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select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY a ALL NULL NULL NULL NULL 10 Using where
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2 DEPENDENT SUBQUERY b ALL NULL NULL NULL NULL 10 Using where
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Warnings:
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Note 1003 select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
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a (select max(a) from t0 b where b.a+a.a<10)
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0 9
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# correlated subquery, explain, while inside the subquery
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set @show_explain_probe_select_id=2;
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set debug='d,show_explain_probe_1';
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select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY a ALL NULL NULL NULL NULL 10 Using where
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2 DEPENDENT SUBQUERY b ALL NULL NULL NULL NULL 10 Using where
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Warnings:
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Note 1003 select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
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a (select max(a) from t0 b where b.a+a.a<10)
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0 9
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# Try to do SHOW EXPLAIN for a query that runs a SET command:
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# I've found experimentally that select_id==2 here...
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#
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set @show_explain_probe_select_id=2;
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set debug='d,show_explain_probe_1';
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set @foo= (select max(a) from t0 where sin(a) >0);
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show explain for $thr2;
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ERROR HY000: Error when executing command SHOW EXPLAIN: Target is not running EXPLAINable command
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#
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# Attempt SHOW EXPLAIN for an UPDATE
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#
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create table t2 as select a as a, a as dummy from t0 limit 2;
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set @show_explain_probe_select_id=2;
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set debug='d,show_explain_probe_1';
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update t2 set dummy=0 where (select max(a) from t0 where t2.a + t0.a <3) >3 ;
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show explain for $thr2;
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ERROR HY000: Error when executing command SHOW EXPLAIN: Target is not running EXPLAINable command
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show explain for $thr2;
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ERROR HY000: Error when executing command SHOW EXPLAIN: Target is not running EXPLAINable command
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drop table t2;
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#
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# Attempt SHOW EXPLAIN for a DELETE
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#
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create table t2 as select a as a, a as dummy from t0 limit 2;
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set @show_explain_probe_select_id=2;
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set debug='d,show_explain_probe_1';
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delete from t2 where (select max(a) from t0 where t2.a + t0.a <3) >3 ;
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show explain for $thr2;
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ERROR HY000: Error when executing command SHOW EXPLAIN: Target is not running EXPLAINable command
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show explain for $thr2;
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ERROR HY000: Error when executing command SHOW EXPLAIN: Target is not running EXPLAINable command
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drop table t2;
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#
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# Multiple SHOW EXPLAIN calls for one select
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#
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create table t2 as select a as a, a as dummy from t0 limit 3;
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set @show_explain_probe_select_id=2;
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set debug='d,show_explain_probe_1';
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select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t2 ALL NULL NULL NULL NULL 3
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2 DEPENDENT SUBQUERY t0 ALL NULL NULL NULL NULL 10 Using where
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Warnings:
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Note 1003 select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t2 ALL NULL NULL NULL NULL 3
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2 DEPENDENT SUBQUERY t0 ALL NULL NULL NULL NULL 10 Using where
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Warnings:
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Note 1003 select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t2 ALL NULL NULL NULL NULL 3
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2 DEPENDENT SUBQUERY t0 ALL NULL NULL NULL NULL 10 Using where
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Warnings:
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Note 1003 select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
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a SUBQ
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0 0
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1 0
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2 0
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drop table t2;
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#
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# SHOW EXPLAIN for SELECT ... ORDER BY with "Using filesort"
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#
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explain select * from t0 order by a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t0 ALL NULL NULL NULL NULL 10 Using filesort
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set debug='d,show_explain_probe_1';
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set @show_explain_probe_select_id=1;
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select * from t0 order by a;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t0 ALL NULL NULL NULL NULL 10 Using filesort
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Warnings:
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Note 1003 select * from t0 order by a
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a
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0
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1
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2
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3
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4
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5
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6
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7
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8
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9
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#
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# SHOW EXPLAIN for SELECT ... with "Using temporary"
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#
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explain select distinct a from t0;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t0 ALL NULL NULL NULL NULL 10 Using temporary
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set debug='d,show_explain_probe_1';
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set @show_explain_probe_select_id=1;
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select distinct a from t0;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t0 ALL NULL NULL NULL NULL 10 Using temporary
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Warnings:
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Note 1003 select distinct a from t0
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a
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0
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1
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2
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3
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4
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5
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#
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# SHOW EXPLAIN for SELECT ... with "Using temporary; Using filesort"
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#
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explain select distinct a from t0;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t0 ALL NULL NULL NULL NULL 10 Using temporary
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set debug='d,show_explain_probe_1';
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set @show_explain_probe_select_id=1;
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select distinct a from t0;
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show explain for $thr2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t0 ALL NULL NULL NULL NULL 10 Using temporary
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Warnings:
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Note 1003 select distinct a from t0
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a
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0
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1
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2
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3
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4
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5
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drop table t0,t1;
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