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drop table if exists t0,t1,t2,t3;
create table t0 (a int);
INSERT INTO t0 VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
# r_filtered=30%, because 3 rows match: 0,1,2
analyze format=json select * from t0 where a<3;
EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "t0",
"access_type": "ALL",
"r_loops": 1,
"rows": 10,
"r_rows": 10,
"filtered": 100,
"r_filtered": 30,
"attached_condition": "(t0.a < 3)"
}
}
}
create table t1 (a int, b int, c int, key(a));
insert into t1 select A.a*10 + B.a, A.a*10 + B.a, A.a*10 + B.a from t0 A, t0 B;
analyze
select * from t0, t1 where t1.a=t0.a and t0.a > 9;
id select_type table type possible_keys key key_len ref rows r_rows filtered r_filtered Extra
1 SIMPLE t0 ALL NULL NULL NULL NULL 10 10 100.00 0.00 Using where
1 SIMPLE t1 ref a a 5 test.t0.a 1 NULL 100.00 NULL
analyze format=json
select * from t0, t1 where t1.a=t0.a and t0.a > 9;
EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "t0",
"access_type": "ALL",
"r_loops": 1,
"rows": 10,
"r_rows": 10,
"filtered": 100,
"r_filtered": 0,
"attached_condition": "((t0.a > 9) and (t0.a is not null))"
},
"table": {
"table_name": "t1",
"access_type": "ref",
"possible_keys": ["a"],
"key": "a",
"key_length": "5",
"used_key_parts": ["a"],
"ref": ["test.t0.a"],
"r_loops": 0,
"rows": 1,
"r_rows": null,
"filtered": 100,
"r_filtered": null
}
}
}
analyze
select * from t0, t1 where t1.a=t0.a and t1.b<4;
id select_type table type possible_keys key key_len ref rows r_rows filtered r_filtered Extra
1 SIMPLE t0 ALL NULL NULL NULL NULL 10 10 100.00 100.00 Using where
1 SIMPLE t1 ref a a 5 test.t0.a 1 1 100.00 40.00 Using where
analyze format=json
select * from t0, t1 where t1.a=t0.a and t1.b<4;
EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "t0",
"access_type": "ALL",
"r_loops": 1,
"rows": 10,
"r_rows": 10,
"filtered": 100,
"r_filtered": 100,
"attached_condition": "(t0.a is not null)"
},
"table": {
"table_name": "t1",
"access_type": "ref",
"possible_keys": ["a"],
"key": "a",
"key_length": "5",
"used_key_parts": ["a"],
"ref": ["test.t0.a"],
"r_loops": 10,
"rows": 1,
"r_rows": 1,
"filtered": 100,
"r_filtered": 40,
"attached_condition": "(t1.b < 4)"
}
}
}
analyze
select * from t1 tbl1, t1 tbl2 where tbl1.b<2 and tbl2.b>5;
id select_type table type possible_keys key key_len ref rows r_rows filtered r_filtered Extra
1 SIMPLE tbl1 ALL NULL NULL NULL NULL 100 100 100.00 2.00 Using where
1 SIMPLE tbl2 ALL NULL NULL NULL NULL 100 100 100.00 94.00 Using where; Using join buffer (flat, BNL join)
analyze format=json
select * from t1 tbl1, t1 tbl2 where tbl1.b<20 and tbl2.b<60;
EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "tbl1",
"access_type": "ALL",
"r_loops": 1,
"rows": 100,
"r_rows": 100,
"filtered": 100,
"r_filtered": 20,
"attached_condition": "(tbl1.b < 20)"
},
"block-nl-join": {
"table": {
"table_name": "tbl2",
"access_type": "ALL",
"r_loops": 1,
"rows": 100,
"r_rows": 100,
"filtered": 100,
"r_filtered": 60,
"attached_condition": "(tbl2.b < 60)"
},
"buffer_type": "flat",
"join_type": "BNL",
"r_filtered": 100
}
}
}
analyze format=json
select * from t1 tbl1, t1 tbl2 where tbl1.b<20 and tbl2.b<60 and tbl1.c > tbl2.c;
EXPLAIN
{
"query_block": {
"select_id": 1,
"table": {
"table_name": "tbl1",
"access_type": "ALL",
"r_loops": 1,
"rows": 100,
"r_rows": 100,
"filtered": 100,
"r_filtered": 20,
"attached_condition": "(tbl1.b < 20)"
},
"block-nl-join": {
"table": {
"table_name": "tbl2",
"access_type": "ALL",
"r_loops": 1,
"rows": 100,
"r_rows": 100,
"filtered": 100,
"r_filtered": 60,
"attached_condition": "(tbl2.b < 60)"
},
"buffer_type": "flat",
"join_type": "BNL",
"attached_condition": "(tbl1.c > tbl2.c)",
"r_filtered": 15.833
}
}
}
drop table t1;
drop table t0;
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