drop table if exists t0, t1, t2, t3, t4;
drop view if exists v1;
SET @old_debug= @@session.debug;
set debug_sync='RESET';
create table t0 (a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1 (a int);
insert into t1 select A.a + 10*B.a + 100*C.a from t0 A, t0 B, t0 C;
alter table t1 add b int, add c int, add filler char(32);
update t1 set b=a, c=a, filler='fooo';
alter table t1 add key(a), add key(b);
show explain format=JSON for;
ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1
explain format=JSON for connection;
ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1
show explain FORMAT=json for 123456789;
ERROR HY000: Unknown thread id: 123456789
explain FORMAT=json for connection 123456789;
ERROR HY000: Unknown thread id: 123456789
show explain FORMAT=json for (select max(a) from t0);
ERROR HY000: You may only use constant expressions in this statement
explain FORMAT=json for connection (select max(a) from t0);
ERROR HY000: You may only use constant expressions in this statement
connect con1, localhost, root,,;
connection con1;
SET @old_debug= @@session.debug;
connection default;
show explain format=JSON for $thr2;
ERROR HY000: Target is not executing an operation with a query plan
explain format=json for connection $thr2;
ERROR HY000: Target is not executing an operation with a query plan
show explain format=json for $thr1;
ERROR HY000: Target is not executing an operation with a query plan
explain FORMAT=JSON for connection $thr1;
ERROR HY000: Target is not executing an operation with a query plan
show explain FORMAT=HTML for $thr1;
ERROR HY000: Unknown EXPLAIN/ANALYZE format name: 'HTML'
explain FORMAT=XML for connection $thr1;
ERROR HY000: Unknown EXPLAIN/ANALYZE format name: 'XML'
connection con1;
set @show_explain_probe_select_id=1;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
select count(*) from t1 where a < 100000;
connection default;
show explain FORMAT=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t1",
"access_type": "range",
"possible_keys": ["a"],
"key": "a",
"key_length": "5",
"used_key_parts": ["a"],
"rows": 999,
"filtered": 100,
"attached_condition": "t1.a < 100000",
"using_index": true
}
}
]
}
}
Warnings:
Note 1003 select count(*) from t1 where a < 100000
connection con1;
count(*)
1000
select max(c) from t1 where a < 10;
connection default;
explain FORMAT=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t1",
"access_type": "range",
"possible_keys": ["a"],
"key": "a",
"key_length": "5",
"used_key_parts": ["a"],
"rows": 10,
"filtered": 100,
"index_condition": "t1.a < 10"
}
}
]
}
}
Warnings:
Note 1003 select max(c) from t1 where a < 10
connection con1;
max(c)
9
select max(c) from t1 where a < 10;
connection default;
explain format=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t1",
"access_type": "range",
"possible_keys": ["a"],
"key": "a",
"key_length": "5",
"used_key_parts": ["a"],
"rows": 10,
"filtered": 100,
"index_condition": "t1.a < 10"
}
}
]
}
}
Warnings:
Note 1003 select max(c) from t1 where a < 10
connection con1;
max(c)
9
# We can catch EXPLAIN, too.
set @show_expl_tmp= @@optimizer_switch;
set optimizer_switch='index_condition_pushdown=on,mrr=on,mrr_sort_keys=on';
explain select max(c) from t1 where a < 10;
connection default;
show explain format=json for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t1",
"access_type": "range",
"possible_keys": ["a"],
"key": "a",
"key_length": "5",
"used_key_parts": ["a"],
"rows": 10,
"filtered": 100,
"index_condition": "t1.a < 10",
"mrr_type": "Rowid-ordered scan"
}
}
]
}
}
Warnings:
Note 1003 explain select max(c) from t1 where a < 10
connection con1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range a a 5 NULL 10 Using index condition; Rowid-ordered scan
# Same for EXPLAIN FOR CONNECTION
explain select max(c) from t1 where a < 10;
connection default;
explain format=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t1",
"access_type": "range",
"possible_keys": ["a"],
"key": "a",
"key_length": "5",
"used_key_parts": ["a"],
"rows": 10,
"filtered": 100,
"index_condition": "t1.a < 10",
"mrr_type": "Rowid-ordered scan"
}
}
]
}
}
Warnings:
Note 1003 explain select max(c) from t1 where a < 10
connection con1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range a a 5 NULL 10 Using index condition; Rowid-ordered scan
set optimizer_switch= @show_expl_tmp;
SET debug_dbug=@old_debug;
# UNION, first branch
set @show_explain_probe_select_id=1;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
explain select a from t0 A union select a+1 from t0 B;
connection default;
show explain format = JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"union_result": {
"table_name": "<union1,2>",
"access_type": "ALL",
"query_specifications": [
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "A",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
]
}
},
{
"query_block": {
"select_id": 2,
"operation": "UNION",
"nested_loop": [
{
"table": {
"table_name": "B",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
]
}
}
]
}
}
}
Warnings:
Note 1003 explain select a from t0 A union select a+1 from t0 B
connection con1;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY A ALL NULL NULL NULL NULL 10
2 UNION B ALL NULL NULL NULL NULL 10
NULL UNION RESULT <union1,2> ALL NULL NULL NULL NULL NULL
SET debug_dbug=@old_debug;
# UNION, second branch
set @show_explain_probe_select_id=2;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
explain select a from t0 A union select a+1 from t0 B;
connection default;
show explain format=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"union_result": {
"table_name": "<union1,2>",
"access_type": "ALL",
"query_specifications": [
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "A",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
]
}
},
{
"query_block": {
"select_id": 2,
"operation": "UNION",
"nested_loop": [
{
"table": {
"table_name": "B",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
]
}
}
]
}
}
}
Warnings:
Note 1003 explain select a from t0 A union select a+1 from t0 B
connection con1;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY A ALL NULL NULL NULL NULL 10
2 UNION B ALL NULL NULL NULL NULL 10
NULL UNION RESULT <union1,2> ALL NULL NULL NULL NULL NULL
SET debug_dbug=@old_debug;
# Uncorrelated subquery, select
set @show_explain_probe_select_id=1;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
select a, (select max(a) from t0 B) from t0 A where a<1;
connection default;
show explain for $thr2;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY A ALL NULL NULL NULL NULL 10 Using where
2 SUBQUERY B ALL NULL NULL NULL NULL 10
Warnings:
Note 1003 select a, (select max(a) from t0 B) from t0 A where a<1
connection con1;
a (select max(a) from t0 B)
0 9
SET debug_dbug=@old_debug;
# Uncorrelated subquery, explain
set @show_explain_probe_select_id=1;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
explain select a, (select max(a) from t0 B) from t0 A where a<1;
connection default;
show explain for $thr2;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY A ALL NULL NULL NULL NULL 10 Using where
2 SUBQUERY B ALL NULL NULL NULL NULL 10
Warnings:
Note 1003 explain select a, (select max(a) from t0 B) from t0 A where a<1
connection con1;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY A ALL NULL NULL NULL NULL 10 Using where
2 SUBQUERY B ALL NULL NULL NULL NULL 10
SET debug_dbug=@old_debug;
# correlated subquery, select
set @show_explain_probe_select_id=1;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
connection default;
show explain for $thr2;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY a ALL NULL NULL NULL NULL 10 Using where
2 DEPENDENT SUBQUERY b ALL NULL NULL NULL NULL 10 Using where
Warnings:
Note 1003 select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
connection con1;
a (select max(a) from t0 b where b.a+a.a<10)
0 9
SET debug_dbug=@old_debug;
# correlated subquery, explain
set @show_explain_probe_select_id=1;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
explain select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
connection default;
show explain for $thr2;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY a ALL NULL NULL NULL NULL 10 Using where
2 DEPENDENT SUBQUERY b ALL NULL NULL NULL NULL 10 Using where
Warnings:
Note 1003 explain select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
connection con1;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY a ALL NULL NULL NULL NULL 10 Using where
2 DEPENDENT SUBQUERY b ALL NULL NULL NULL NULL 10 Using where
SET debug_dbug=@old_debug;
# correlated subquery, select, while inside the subquery
set @show_explain_probe_select_id=2;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
connection default;
show explain format=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "a",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "a.a < 1"
}
}
],
"subqueries": [
{
"expression_cache": {
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "b",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "b.a + a.a < 10"
}
}
]
}
}
}
]
}
}
Warnings:
Note 1003 select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
connection con1;
a (select max(a) from t0 b where b.a+a.a<10)
0 9
SET debug_dbug=@old_debug;
# correlated subquery, explain, while inside the subquery
set @show_explain_probe_select_id=2;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
connection default;
show explain format=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "a",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "a.a < 1"
}
}
],
"subqueries": [
{
"expression_cache": {
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "b",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "b.a + a.a < 10"
}
}
]
}
}
}
]
}
}
Warnings:
Note 1003 select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
connection con1;
a (select max(a) from t0 b where b.a+a.a<10)
0 9
SET debug_dbug=@old_debug;
# correlated subquery, explain, while inside the subquery
set @show_explain_probe_select_id=1;
SET debug_dbug='+d,show_explain_probe_join_exec_end';
select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1;
connection default;
show explain format=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "a",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "a.a < 1"
}
}
],
"subqueries": [
{
"expression_cache": {
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "b",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "b.a + a.a < 10"
}
}
]
}
}
}
]
}
}
Warnings:
Note 1003 select a, (select max(a) from t0 b where b.a+a.a<10) from t0 a where a<1
connection con1;
a (select max(a) from t0 b where b.a+a.a<10)
0 9
SET debug_dbug=@old_debug;
# Try to do SHOW EXPLAIN for a query that runs a SET command:
# I've found experimentally that select_id==2 here...
#
create table t2 (a int);
insert into t2 values (1),(2);
set @show_explain_probe_select_id=3;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
set @foo= (select max(a) from t2
where a + (select max(a) from t0 where t0.a>t2.a) < 10000);
connection default;
show explain format=JSON for $thr2;
ERROR HY000: Target is not executing an operation with a query plan
kill query $thr2;
connection con1;
ERROR 70100: Query execution was interrupted
SET debug_dbug=@old_debug;
drop table t2;
#
# Attempt SHOW EXPLAIN for an UPDATE
#
create table t2 as select a as a, a as dummy from t0 limit 2;
set @show_explain_probe_select_id=2;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
update t2 set dummy=0 where (select max(a) from t0 where t2.a + t0.a <3) >3 ;
connection default;
show explain format=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"update": 1,
"table_name": "t2",
"access_type": "ALL",
"rows": 2,
"attached_condition": "(subquery#2) > 3"
},
"subqueries": [
{
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
]
}
}
Warnings:
Note 1003 update t2 set dummy=0 where (select max(a) from t0 where t2.a + t0.a <3) >3
show explain format=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"update": 1,
"table_name": "t2",
"access_type": "ALL",
"rows": 2,
"attached_condition": "(subquery#2) > 3"
},
"subqueries": [
{
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
]
}
}
Warnings:
Note 1003 update t2 set dummy=0 where (select max(a) from t0 where t2.a + t0.a <3) >3
connection con1;
#
# EXPLAIN FOR CONNECTION for an UPDATE
#
set @show_explain_probe_select_id=2;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
update t2 set dummy=0 where (select max(a) from t0 where t2.a + t0.a <3) >3 ;
connection default;
explain format=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"update": 1,
"table_name": "t2",
"access_type": "ALL",
"rows": 2,
"attached_condition": "(subquery#2) > 3"
},
"subqueries": [
{
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
]
}
}
Warnings:
Note 1003 update t2 set dummy=0 where (select max(a) from t0 where t2.a + t0.a <3) >3
explain format=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"update": 1,
"table_name": "t2",
"access_type": "ALL",
"rows": 2,
"attached_condition": "(subquery#2) > 3"
},
"subqueries": [
{
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
]
}
}
Warnings:
Note 1003 update t2 set dummy=0 where (select max(a) from t0 where t2.a + t0.a <3) >3
connection con1;
drop table t2;
SET debug_dbug=@old_debug;
#
# Attempt SHOW EXPLAIN for a DELETE
#
create table t2 as select a as a, a as dummy from t0 limit 2;
set @show_explain_probe_select_id=2;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
delete from t2 where (select max(a) from t0 where t2.a + t0.a <3) >3 ;
connection default;
show explain format=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"delete": 1,
"table_name": "t2",
"access_type": "ALL",
"rows": 2,
"attached_condition": "(subquery#2) > 3"
},
"subqueries": [
{
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
]
}
}
Warnings:
Note 1003 delete from t2 where (select max(a) from t0 where t2.a + t0.a <3) >3
show explain format=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"delete": 1,
"table_name": "t2",
"access_type": "ALL",
"rows": 2,
"attached_condition": "(subquery#2) > 3"
},
"subqueries": [
{
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
]
}
}
Warnings:
Note 1003 delete from t2 where (select max(a) from t0 where t2.a + t0.a <3) >3
connection con1;
drop table t2;
SET debug_dbug=@old_debug;
#
# Attempt EXPLAIN FOR CONNECTION for a DELETE
#
create table t2 as select a as a, a as dummy from t0 limit 2;
set @show_explain_probe_select_id=2;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
delete from t2 where (select max(a) from t0 where t2.a + t0.a <3) >3 ;
connection default;
explain format=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"delete": 1,
"table_name": "t2",
"access_type": "ALL",
"rows": 2,
"attached_condition": "(subquery#2) > 3"
},
"subqueries": [
{
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
]
}
}
Warnings:
Note 1003 delete from t2 where (select max(a) from t0 where t2.a + t0.a <3) >3
explain format=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"delete": 1,
"table_name": "t2",
"access_type": "ALL",
"rows": 2,
"attached_condition": "(subquery#2) > 3"
},
"subqueries": [
{
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
]
}
}
Warnings:
Note 1003 delete from t2 where (select max(a) from t0 where t2.a + t0.a <3) >3
connection con1;
drop table t2;
SET debug_dbug=@old_debug;
#
# Multiple SHOW EXPLAIN calls for one select
#
create table t2 as select a as a, a as dummy from t0 limit 3;
set @show_explain_probe_select_id=2;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2;
connection default;
show explain format=json for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t2",
"access_type": "ALL",
"rows": 3,
"filtered": 100
}
}
],
"subqueries": [
{
"expression_cache": {
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
}
]
}
}
Warnings:
Note 1003 select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
show explain format=json for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t2",
"access_type": "ALL",
"rows": 3,
"filtered": 100
}
}
],
"subqueries": [
{
"expression_cache": {
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
}
]
}
}
Warnings:
Note 1003 select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
show explain format=json for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t2",
"access_type": "ALL",
"rows": 3,
"filtered": 100
}
}
],
"subqueries": [
{
"expression_cache": {
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
}
]
}
}
Warnings:
Note 1003 select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
connection con1;
a SUBQ
0 0
1 0
2 0
drop table t2;
SET debug_dbug=@old_debug;
#
# Multiple EXPLAIN FOR CONNECTION calls for one select
#
create table t2 as select a as a, a as dummy from t0 limit 3;
set @show_explain_probe_select_id=2;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2;
connection default;
explain format=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t2",
"access_type": "ALL",
"rows": 3,
"filtered": 100
}
}
],
"subqueries": [
{
"expression_cache": {
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
}
]
}
}
Warnings:
Note 1003 select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
explain format=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t2",
"access_type": "ALL",
"rows": 3,
"filtered": 100
}
}
],
"subqueries": [
{
"expression_cache": {
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
}
]
}
}
Warnings:
Note 1003 select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
explain format=JSON for connection $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t2",
"access_type": "ALL",
"rows": 3,
"filtered": 100
}
}
],
"subqueries": [
{
"expression_cache": {
"query_block": {
"select_id": 2,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t2.a + t0.a < 3"
}
}
]
}
}
}
]
}
}
Warnings:
Note 1003 select t2.a, ((select max(a) from t0 where t2.a + t0.a <3) >3) as SUBQ from t2
connection con1;
a SUBQ
0 0
1 0
2 0
drop table t2;
SET debug_dbug=@old_debug;
#
# SHOW EXPLAIN for SELECT ... ORDER BY with "Using filesort"
#
explain select * from t0 order by a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 ALL NULL NULL NULL NULL 10 Using filesort
SET debug_dbug='+d,show_explain_probe_join_exec_start';
set @show_explain_probe_select_id=1;
select * from t0 order by a;
connection default;
show explain format=json for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"read_sorted_file": {
"filesort": {
"sort_key": "t0.a",
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
}
}
]
}
}
Warnings:
Note 1003 select * from t0 order by a
connection con1;
a
0
1
2
3
4
5
6
7
8
9
SET debug_dbug=@old_debug;
#
# SHOW EXPLAIN for SELECT ... with "Using temporary"
#
connection default;
explain select distinct a from t0;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 ALL NULL NULL NULL NULL 10 Using temporary
connection con1;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
set @show_explain_probe_select_id=1;
select distinct a from t0;
connection default;
show explain format=json for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"temporary_table": {
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
]
}
}
}
Warnings:
Note 1003 select distinct a from t0
connection con1;
a
0
1
2
3
4
5
6
7
8
9
SET debug_dbug=@old_debug;
#
# SHOW EXPLAIN for SELECT ... with "Using temporary; Using filesort"
#
connection default;
explain select distinct a from t0;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 ALL NULL NULL NULL NULL 10 Using temporary
connection con1;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
set @show_explain_probe_select_id=1;
select distinct a from t0;
connection default;
show explain format=json for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"temporary_table": {
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100
}
}
]
}
}
}
Warnings:
Note 1003 select distinct a from t0
connection con1;
a
0
1
2
3
4
5
6
7
8
9
SET debug_dbug=@old_debug;
#
# Check if queries in non-default charsets work.
#
set names cp1251;
select charset('��');
charset('��')
cp1251
select hex('��');
hex('��')
E3FB
set @show_explain_probe_select_id=1;
SET debug_dbug='+d,show_explain_probe_join_exec_start';
select * from t0 where length('��') = a;
connection default;
set names utf8;
show explain format=JSON for $thr2;
SHOW EXPLAIN
{
"query_block": {
"select_id": 1,
"nested_loop": [
{
"table": {
"table_name": "t0",
"access_type": "ALL",
"rows": 10,
"filtered": 100,
"attached_condition": "t0.a = <cache>(octet_length('гы'))"
}
}
]
}
}
Warnings:
Note 1003 select * from t0 where length('гы') = a
set names default;
connection con1;
a
2
SET debug_dbug=@old_debug;
set names default;
drop table if exists t0,t1,t2;
Warnings:
Note 1051 Unknown table 'test.t2'
#
# MDEV-28124: Server crashes in Explain_aggr_filesort::print_json_members
# upon SHOW ANALYZE/EXPLAIN FORMAT=JSON
#
connection con1;
set @show_explain_probe_query= 'SELECT count(*) - count(*) FROM sys.waits_by_user_by_latency';
set debug_dbug='+d,explain_notify_tables_are_closed';
SELECT count(*) - count(*) FROM sys.waits_by_user_by_latency;
connection default;
SHOW EXPLAIN FORMAT=JSON FOR $thr2;
ERROR HY000: Target is not executing an operation with a query plan
connection con1;
count(*) - count(*)
0
# End
connection default;
disconnect con1;
set debug_sync='RESET';