mariadb/mysql-test/r/explain_json.result

drop table if exists t0,t1,t2;
create table t0(a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
explain format=json select * from t0;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t0",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100
    }
  }
}
explain format=json select * from t0 where 1>2;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE"
    }
  }
}
explain format=json select * from t0 where a<3;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t0",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100,
      "attached_condition": "(t0.a < 3)"
    }
  }
}
# Try a basic join
create table t1 (a int, b int, filler char(32), key(a));
insert into t1 
select 
a.a + b.a* 10 + c.a * 100, 
a.a + b.a* 10 + c.a * 100,
'filler'
from t0 a, t0 b, t0 c;
explain format=json select * from t0,t1 where t1.a=t0.a;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t0",
      "access_type": "ALL",
      "rows": 10,
      "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"],
      "rows": 1,
      "filtered": 100
    }
  }
}
# Try range and index_merge
create table t2 (a1 int, a2 int, b1 int, b2 int, key(a1,a2), key(b1,b2));
insert into t2 select a,a,a,a from t1;
explain format=json select * from t2 where a1<5;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t2",
      "access_type": "range",
      "possible_keys": ["a1"],
      "key": "a1",
      "key_length": "5",
      "used_key_parts": ["a1"],
      "rows": 5,
      "filtered": 100,
      "index_condition": "(t2.a1 < 5)"
    }
  }
}
explain format=json select * from t2 where a1=1 or b1=2;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t2",
      "access_type": "index_merge",
      "possible_keys": ["a1", "b1"],
      "key_length": "5,5",
      "index_merge": {
        "sort_union": {
          "range": {
            "key": "a1",
            "used_key_parts": ["a1"]
          },
          "range": {
            "key": "b1",
            "used_key_parts": ["b1"]
          }
        }
      },
      "rows": 2,
      "filtered": 100,
      "attached_condition": "((t2.a1 = 1) or (t2.b1 = 2))"
    }
  }
}
explain format=json select * from t2 where a1=1 or (b1=2 and b2=3);
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t2",
      "access_type": "index_merge",
      "possible_keys": ["a1", "b1"],
      "key_length": "5,10",
      "index_merge": {
        "sort_union": {
          "range": {
            "key": "a1",
            "used_key_parts": ["a1"]
          },
          "range": {
            "key": "b1",
            "used_key_parts": ["b1", "b2"]
          }
        }
      },
      "rows": 2,
      "filtered": 100,
      "attached_condition": "((t2.a1 = 1) or ((t2.b1 = 2) and (t2.b2 = 3)))"
    }
  }
}
explain format=json select * from t2 where (a1=1 and a2=1) or 
(b1=2 and b2=1);
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t2",
      "access_type": "index_merge",
      "possible_keys": ["a1", "b1"],
      "key_length": "10,10",
      "index_merge": {
        "union": {
          "range": {
            "key": "a1",
            "used_key_parts": ["a1", "a2"]
          },
          "range": {
            "key": "b1",
            "used_key_parts": ["b1", "b2"]
          }
        }
      },
      "rows": 2,
      "filtered": 100,
      "attached_condition": "(((t2.a1 = 1) and (t2.a2 = 1)) or ((t2.b1 = 2) and (t2.b2 = 1)))"
    }
  }
}
# Try ref access on two key components
explain format=json select * from t0,t2 where t2.b1=t0.a and t2.b2=4;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t0",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100,
      "attached_condition": "(t0.a is not null)"
    },
    "table": {
      "table_name": "t2",
      "access_type": "ref",
      "possible_keys": ["b1"],
      "key": "b1",
      "key_length": "10",
      "used_key_parts": ["b1", "b2"],
      "ref": ["test.t0.a", "const"],
      "rows": 1,
      "filtered": 100
    }
  }
}
drop table t1,t2;
#
# Try a UNION
#
explain format=json select * from t0 A union     select * from t0 B;
EXPLAIN
{
  "query_block": {
    "union_result": {
      "table_name": "<union1,2>",
      "access_type": "ALL",
      "query_specifications": [
        {
          "query_block": {
            "select_id": 1,
            "table": {
              "table_name": "A",
              "access_type": "ALL",
              "rows": 10,
              "filtered": 100
            }
          }
        },
        {
          "query_block": {
            "select_id": 2,
            "table": {
              "table_name": "B",
              "access_type": "ALL",
              "rows": 10,
              "filtered": 100
            }
          }
        }
      ]
    }
  }
}
explain format=json select * from t0 A union all select * from t0 B;
EXPLAIN
{
  "query_block": {
    "union_result": {
      "table_name": "<union1,2>",
      "access_type": "ALL",
      "query_specifications": [
        {
          "query_block": {
            "select_id": 1,
            "table": {
              "table_name": "A",
              "access_type": "ALL",
              "rows": 10,
              "filtered": 100
            }
          }
        },
        {
          "query_block": {
            "select_id": 2,
            "table": {
              "table_name": "B",
              "access_type": "ALL",
              "rows": 10,
              "filtered": 100
            }
          }
        }
      ]
    }
  }
}
#
# Subqueries
#
create table t1 (a int, b int);
insert into t1 select a,a from t0;
explain format=json select a, a > (select max(b) from t1 where t1.b=t0.a) from t0;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t0",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100
    },
    "subqueries": [
      {
        "expression_cache": {
          "state": "uninitialized",
          "query_block": {
            "select_id": 2,
            "table": {
              "table_name": "t1",
              "access_type": "ALL",
              "rows": 10,
              "filtered": 100,
              "attached_condition": "(t1.b = t0.a)"
            }
          }
        }
      }
    ]
  }
}
explain format=json 
select * from t0 where 
a > (select max(b) from t1 where t1.b=t0.a) or a < 3 ;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t0",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100,
      "attached_condition": "((t0.a > (subquery#2)) or (t0.a < 3))"
    },
    "subqueries": [
      {
        "expression_cache": {
          "state": "uninitialized",
          "query_block": {
            "select_id": 2,
            "table": {
              "table_name": "t1",
              "access_type": "ALL",
              "rows": 10,
              "filtered": 100,
              "attached_condition": "(t1.b = t0.a)"
            }
          }
        }
      }
    ]
  }
}
drop table t1;
#
# Join buffering
#
create table t1 (a int, b int);
insert into t1 select tbl1.a+10*tbl2.a, tbl1.a+10*tbl2.a from t0 tbl1, t0 tbl2;
explain format=json
select * from t1 tbl1, t1 tbl2 where tbl1.a=tbl2.a and tbl1.b < 3 and tbl2.b < 5;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "tbl1",
      "access_type": "ALL",
      "rows": 100,
      "filtered": 100,
      "attached_condition": "(tbl1.b < 3)"
    },
    "block-nl-join": {
      "table": {
        "table_name": "tbl2",
        "access_type": "ALL",
        "rows": 100,
        "filtered": 100,
        "attached_condition": "(tbl2.b < 5)"
      },
      "buffer_type": "flat",
      "buffer_size": "256Kb",
      "join_type": "BNL",
      "attached_condition": "(tbl2.a = tbl1.a)"
    }
  }
}
drop table t1;
#
# Single-table UPDATE/DELETE, INSERT
#
explain format=json delete from t0;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Deleting all rows"
    }
  }
}
explain format=json delete from t0 where 1 > 2;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE"
    }
  }
}
explain format=json delete from t0 where a < 3;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "delete": 1,
      "table_name": "t0",
      "access_type": "ALL",
      "rows": 10,
      "attached_condition": "(t0.a < 3)"
    }
  }
}
explain format=json update t0 set a=3 where a in (2,3,4);
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "update": 1,
      "table_name": "t0",
      "access_type": "ALL",
      "rows": 10,
      "attached_condition": "(t0.a in (2,3,4))"
    }
  }
}
explain format=json insert into t0 values (1);
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t0"
    }
  }
}
create table t1 like t0;
explain format=json insert into t1 values ((select max(a) from t0));
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t1"
    },
    "subqueries": [
      {
        "query_block": {
          "select_id": 2,
          "table": {
            "table_name": "t0",
            "access_type": "ALL",
            "rows": 10,
            "filtered": 100
          }
        }
      }
    ]
  }
}
drop table t1;
#
# A derived table
#
create table t1 (a int, b int);
insert into t1 select a,a from t0;
explain format=json
select * from (select a, count(*) as cnt from t1 group by a) as tbl
where cnt>0;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "<derived2>",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100,
      "attached_condition": "(tbl.cnt > 0)",
      "materialized": {
        "query_block": {
          "select_id": 2,
          "filesort": {
            "temporary_table": {
              "function": "buffer",
              "table": {
                "table_name": "t1",
                "access_type": "ALL",
                "rows": 10,
                "filtered": 100
              }
            }
          }
        }
      }
    }
  }
}
explain format=json
select * from (select a, count(*) as cnt from t1 group by a) as tbl1, t1 as
tbl2 where cnt=tbl2.a;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "tbl2",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100,
      "attached_condition": "(tbl2.a is not null)"
    },
    "table": {
      "table_name": "<derived2>",
      "access_type": "ref",
      "possible_keys": ["key0"],
      "key": "key0",
      "key_length": "8",
      "used_key_parts": ["cnt"],
      "ref": ["test.tbl2.a"],
      "rows": 2,
      "filtered": 100,
      "attached_condition": "(tbl1.cnt = tbl2.a)",
      "materialized": {
        "query_block": {
          "select_id": 2,
          "filesort": {
            "temporary_table": {
              "function": "buffer",
              "table": {
                "table_name": "t1",
                "access_type": "ALL",
                "rows": 10,
                "filtered": 100
              }
            }
          }
        }
      }
    }
  }
}
#
# Non-merged semi-join (aka JTBM)
#
explain format=json 
select * from t1 where a in (select max(a) from t1 group by b);
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t1",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100,
      "attached_condition": "(t1.a is not null)"
    },
    "table": {
      "table_name": "<subquery2>",
      "access_type": "eq_ref",
      "possible_keys": ["distinct_key"],
      "key": "distinct_key",
      "key_length": "4",
      "used_key_parts": ["max(a)"],
      "ref": ["test.t1.a"],
      "rows": 1,
      "filtered": 100,
      "materialized": {
        "unique": 1,
        "query_block": {
          "select_id": 2,
          "temporary_table": {
            "function": "buffer",
            "table": {
              "table_name": "t1",
              "access_type": "ALL",
              "rows": 10,
              "filtered": 100
            }
          }
        }
      }
    }
  }
}
#
# Semi-join Materialization
#
create table t2 like t1;
insert into t2 select * from t1;
explain format=json
select * from t1,t2 where t1.a in ( select a from t0);
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "const_condition": "1",
    "table": {
      "table_name": "t1",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100
    },
    "table": {
      "table_name": "<subquery2>",
      "access_type": "eq_ref",
      "possible_keys": ["distinct_key"],
      "key": "distinct_key",
      "key_length": "4",
      "used_key_parts": ["a"],
      "ref": ["func"],
      "rows": 1,
      "filtered": 100,
      "materialized": {
        "unique": 1,
        "query_block": {
          "select_id": 2,
          "table": {
            "table_name": "t0",
            "access_type": "ALL",
            "rows": 10,
            "filtered": 100
          }
        }
      }
    },
    "block-nl-join": {
      "table": {
        "table_name": "t2",
        "access_type": "ALL",
        "rows": 10,
        "filtered": 100
      },
      "buffer_type": "flat",
      "buffer_size": "256Kb",
      "join_type": "BNL"
    }
  }
}
# 
# First-Match
# 
explain
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	10	
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	Using where; FirstMatch(t2); Using join buffer (flat, BNL join)
explain format=json
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t2",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100
    },
    "block-nl-join": {
      "table": {
        "table_name": "t1",
        "access_type": "ALL",
        "rows": 10,
        "filtered": 100,
        "first_match": "t2"
      },
      "buffer_type": "flat",
      "buffer_size": "256Kb",
      "join_type": "BNL",
      "attached_condition": "((t1.b = t2.b) and (t1.a = t2.a))"
    }
  }
}
# 
# Duplicate Weedout
# 
set @tmp= @@optimizer_switch;
set optimizer_switch='firstmatch=off';
explain
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	10	
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	10	Using where; Start temporary; End temporary; Using join buffer (flat, BNL join)
explain format=json
select * from t2 where t2.a in ( select a from t1 where t1.b=t2.b);
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t2",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100
    },
    "duplicates_removal": {
      "block-nl-join": {
        "table": {
          "table_name": "t1",
          "access_type": "ALL",
          "rows": 10,
          "filtered": 100
        },
        "buffer_type": "flat",
        "buffer_size": "256Kb",
        "join_type": "BNL",
        "attached_condition": "((t1.b = t2.b) and (t1.a = t2.a))"
      }
    }
  }
}
set optimizer_switch=@tmp;
drop table t1,t2;
#
# MRR for range access (no BKA, just MRR)
#
create table t1 (a int, b int, key(a));
insert into t1 select tbl1.a+10*tbl2.a, 12345 from t0 tbl1, t0 tbl2;
set @tmp= @@optimizer_switch;
set optimizer_switch='mrr=on,mrr_sort_keys=on';
explain format=json select * from t1 where a < 3;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t1",
      "access_type": "range",
      "possible_keys": ["a"],
      "key": "a",
      "key_length": "5",
      "used_key_parts": ["a"],
      "rows": 1,
      "filtered": 100,
      "index_condition": "(t1.a < 3)",
      "mrr_type": "Rowid-ordered scan"
    }
  }
}
# 'Range checked for each record'
set optimizer_switch=@tmp;
explain format=json
select * from t1 tbl1, t1 tbl2 where tbl2.a < tbl1.b;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "tbl1",
      "access_type": "ALL",
      "rows": 100,
      "filtered": 100
    },
    "range-checked-for-each-record": {
      "keys": ["a"],
      "table": {
        "table_name": "tbl2",
        "access_type": "ALL",
        "possible_keys": ["a"],
        "rows": 100,
        "filtered": 100
      }
    }
  }
}
drop table t1;
drop table t0;
#
# MDEV-7265: "Full scan on NULL key", the join case
#
CREATE TABLE t1 (a INT, KEY(a));
INSERT INTO t1 VALUES (1),(2);
CREATE TABLE t2 (b INT);
INSERT INTO t2 VALUES (3),(4);
EXPLAIN FORMAT=JSON SELECT * FROM t1 AS outer_t1 WHERE a <> ALL ( SELECT a FROM t1, t2 WHERE b <> outer_t1.a );
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "outer_t1",
      "access_type": "index",
      "key": "a",
      "key_length": "5",
      "used_key_parts": ["a"],
      "rows": 2,
      "filtered": 100,
      "attached_condition": "(not(<in_optimizer>(outer_t1.a,<exists>(subquery#2))))",
      "using_index": true
    },
    "subqueries": [
      {
        "query_block": {
          "select_id": 2,
          "full-scan-on-null_key": {
            "table": {
              "table_name": "t1",
              "access_type": "ref_or_null",
              "possible_keys": ["a"],
              "key": "a",
              "key_length": "5",
              "used_key_parts": ["a"],
              "ref": ["func"],
              "rows": 2,
              "filtered": 100,
              "attached_condition": "trigcond(((<cache>(outer_t1.a) = t1.a) or isnull(t1.a)))",
              "using_index": true
            }
          },
          "block-nl-join": {
            "table": {
              "table_name": "t2",
              "access_type": "ALL",
              "rows": 2,
              "filtered": 100
            },
            "buffer_type": "flat",
            "buffer_size": "256Kb",
            "join_type": "BNL",
            "attached_condition": "((t2.b <> outer_t1.a) and trigcond(((<cache>(outer_t1.a) = t1.a) or isnull(t1.a))))"
          }
        }
      }
    ]
  }
}
DROP TABLE t1,t2;
#
# Join's constant expression
#
create table t0(a int);
insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1(a int, b int);
insert into t1 select tbl1.a+10*tbl2.a, 1234 from t0 tbl1, t0 tbl2;
explain format=json 
select * from t0 
where 
20000 > all (select max(tbl1.a + tbl2.a)
from t1 tbl1, t1 tbl2 where tbl1.b=tbl2.b);
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "const_condition": "<not>(<in_optimizer>(20000,(<max>(subquery#2) >= 20000)))",
    "table": {
      "table_name": "t0",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100
    },
    "subqueries": [
      {
        "query_block": {
          "select_id": 2,
          "table": {
            "table_name": "tbl1",
            "access_type": "ALL",
            "rows": 100,
            "filtered": 100
          },
          "block-nl-join": {
            "table": {
              "table_name": "tbl2",
              "access_type": "ALL",
              "rows": 100,
              "filtered": 100
            },
            "buffer_type": "flat",
            "buffer_size": "256Kb",
            "join_type": "BNL",
            "attached_condition": "(tbl2.b = tbl1.b)"
          }
        }
      }
    ]
  }
}
drop table t1;
drop table t0;
# 
# MDEV-7264: Assertion `0' failed in subselect_engine::get_identifier() on EXPLAIN JSON
# 
CREATE TABLE t1 (a INT);
INSERT INTO t1 VALUES (1),(2);
CREATE TABLE t2 (b INT);
INSERT INTO t2 VALUES (3),(4);
EXPLAIN FORMAT=JSON SELECT * FROM t1 WHERE a <> ALL ( SELECT b FROM t2 );
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t1",
      "access_type": "ALL",
      "rows": 2,
      "filtered": 100,
      "attached_condition": "(not(<in_optimizer>(t1.a,t1.a in (subquery#2))))"
    },
    "subqueries": [
      {
        "query_block": {
          "select_id": 2,
          "table": {
            "table_name": "t2",
            "access_type": "ALL",
            "rows": 2,
            "filtered": 100
          }
        }
      }
    ]
  }
}
DROP TABLE t1, t2;
#
# MDEV-7927: Server crashes in in Time_and_counter_tracker::incr_loops
#
CREATE TABLE t1 (i INT);
INSERT INTO t1 VALUES (1),(2);
EXPLAIN SELECT * FROM t1 WHERE 3 IN ( SELECT 4 UNION SELECT 5 );
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	Impossible WHERE
2	SUBQUERY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
3	UNION	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
NULL	UNION RESULT	<union2,3>	ALL	NULL	NULL	NULL	NULL	NULL	
DROP TABLE t1;
#
# MDEV-7860: EXPLAIN FORMAT=JSON crashes for loose scan query
#
create table t2(a int);
insert into t2 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t1 (a int, b int, c int, d int, key(a,b,c));
insert into t1 select  A.a, B.a, C.a, D.a from t2 A, t2 B, t2 C, t2 D;
explain select count(distinct b) from t1 group by a;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	NULL	a	10	NULL	101	Using index for group-by
explain format=json select count(distinct b) from t1 group by a;
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t1",
      "access_type": "range",
      "key": "a",
      "key_length": "10",
      "used_key_parts": ["a", "b"],
      "rows": 101,
      "filtered": 100,
      "using_index_for_group_by": true
    }
  }
}
analyze format=json select count(distinct b) from t1 group by a;
ANALYZE
{
  "query_block": {
    "select_id": 1,
    "r_loops": 1,
    "r_total_time_ms": "REPLACED",
    "table": {
      "table_name": "t1",
      "access_type": "range",
      "key": "a",
      "key_length": "10",
      "used_key_parts": ["a", "b"],
      "r_loops": 1,
      "rows": 101,
      "r_rows": 100,
      "r_total_time_ms": "REPLACED",
      "filtered": 100,
      "r_filtered": 100,
      "using_index_for_group_by": true
    }
  }
}
drop table t1,t2;
#
# Try both variants of LooseScan (data/queries borrowed from group_min_max.test)
#
create table t1 (
a1 char(64), a2 char(64), b char(16), c char(16) not null, d char(16), dummy char(248) default ' '
);
insert into t1 (a1, a2, b, c, d) values
('a','a','a','a111','xy1'),('a','a','a','b111','xy2'),('a','a','a','c111','xy3'),('a','a','a','d111','xy4'),
('a','a','b','e112','xy1'),('a','a','b','f112','xy2'),('a','a','b','g112','xy3'),('a','a','b','h112','xy4'),
('a','b','a','i121','xy1'),('a','b','a','j121','xy2'),('a','b','a','k121','xy3'),('a','b','a','l121','xy4'),
('a','b','b','m122','xy1'),('a','b','b','n122','xy2'),('a','b','b','o122','xy3'),('a','b','b','p122','xy4'),
('b','a','a','a211','xy1'),('b','a','a','b211','xy2'),('b','a','a','c211','xy3'),('b','a','a','d211','xy4'),
('b','a','b','e212','xy1'),('b','a','b','f212','xy2'),('b','a','b','g212','xy3'),('b','a','b','h212','xy4'),
('b','b','a','i221','xy1'),('b','b','a','j221','xy2'),('b','b','a','k221','xy3'),('b','b','a','l221','xy4'),
('b','b','b','m222','xy1'),('b','b','b','n222','xy2'),('b','b','b','o222','xy3'),('b','b','b','p222','xy4'),
('c','a','a','a311','xy1'),('c','a','a','b311','xy2'),('c','a','a','c311','xy3'),('c','a','a','d311','xy4'),
('c','a','b','e312','xy1'),('c','a','b','f312','xy2'),('c','a','b','g312','xy3'),('c','a','b','h312','xy4'),
('c','b','a','i321','xy1'),('c','b','a','j321','xy2'),('c','b','a','k321','xy3'),('c','b','a','l321','xy4'),
('c','b','b','m322','xy1'),('c','b','b','n322','xy2'),('c','b','b','o322','xy3'),('c','b','b','p322','xy4'),
('d','a','a','a411','xy1'),('d','a','a','b411','xy2'),('d','a','a','c411','xy3'),('d','a','a','d411','xy4'),
('d','a','b','e412','xy1'),('d','a','b','f412','xy2'),('d','a','b','g412','xy3'),('d','a','b','h412','xy4'),
('d','b','a','i421','xy1'),('d','b','a','j421','xy2'),('d','b','a','k421','xy3'),('d','b','a','l421','xy4'),
('d','b','b','m422','xy1'),('d','b','b','n422','xy2'),('d','b','b','o422','xy3'),('d','b','b','p422','xy4'),
('a','a','a','a111','xy1'),('a','a','a','b111','xy2'),('a','a','a','c111','xy3'),('a','a','a','d111','xy4'),
('a','a','b','e112','xy1'),('a','a','b','f112','xy2'),('a','a','b','g112','xy3'),('a','a','b','h112','xy4'),
('a','b','a','i121','xy1'),('a','b','a','j121','xy2'),('a','b','a','k121','xy3'),('a','b','a','l121','xy4'),
('a','b','b','m122','xy1'),('a','b','b','n122','xy2'),('a','b','b','o122','xy3'),('a','b','b','p122','xy4'),
('b','a','a','a211','xy1'),('b','a','a','b211','xy2'),('b','a','a','c211','xy3'),('b','a','a','d211','xy4'),
('b','a','b','e212','xy1'),('b','a','b','f212','xy2'),('b','a','b','g212','xy3'),('b','a','b','h212','xy4'),
('b','b','a','i221','xy1'),('b','b','a','j221','xy2'),('b','b','a','k221','xy3'),('b','b','a','l221','xy4'),
('b','b','b','m222','xy1'),('b','b','b','n222','xy2'),('b','b','b','o222','xy3'),('b','b','b','p222','xy4'),
('c','a','a','a311','xy1'),('c','a','a','b311','xy2'),('c','a','a','c311','xy3'),('c','a','a','d311','xy4'),
('c','a','b','e312','xy1'),('c','a','b','f312','xy2'),('c','a','b','g312','xy3'),('c','a','b','h312','xy4'),
('c','b','a','i321','xy1'),('c','b','a','j321','xy2'),('c','b','a','k321','xy3'),('c','b','a','l321','xy4'),
('c','b','b','m322','xy1'),('c','b','b','n322','xy2'),('c','b','b','o322','xy3'),('c','b','b','p322','xy4'),
('d','a','a','a411','xy1'),('d','a','a','b411','xy2'),('d','a','a','c411','xy3'),('d','a','a','d411','xy4'),
('d','a','b','e412','xy1'),('d','a','b','f412','xy2'),('d','a','b','g412','xy3'),('d','a','b','h412','xy4'),
('d','b','a','i421','xy1'),('d','b','a','j421','xy2'),('d','b','a','k421','xy3'),('d','b','a','l421','xy4'),
('d','b','b','m422','xy1'),('d','b','b','n422','xy2'),('d','b','b','o422','xy3'),('d','b','b','p422','xy4');
create index idx_t1_0 on t1 (a1);
create index idx_t1_1 on t1 (a1,a2,b,c);
create index idx_t1_2 on t1 (a1,a2,b);
analyze table t1;
Table	Op	Msg_type	Msg_text
test.t1	analyze	status	Table is already up to date
explain select count(distinct a1,a2,b) from t1 where (a2 >= 'b') and (b = 'a');
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	NULL	idx_t1_1	147	NULL	17	Using where; Using index for group-by
explain select count(distinct a1,a2,b,c) from t1 where (a2 >= 'b') and (b = 'a') and (c = 'i121');
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	range	NULL	idx_t1_1	163	NULL	65	Using where; Using index for group-by (scanning)
explain format=json select count(distinct a1,a2,b) from t1 where (a2 >= 'b') and (b = 'a');
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t1",
      "access_type": "range",
      "key": "idx_t1_1",
      "key_length": "147",
      "used_key_parts": ["a1", "a2", "b"],
      "rows": 17,
      "filtered": 100,
      "attached_condition": "((t1.b = 'a') and (t1.a2 >= 'b'))",
      "using_index_for_group_by": true
    }
  }
}
explain format=json select count(distinct a1,a2,b,c) from t1 where (a2 >= 'b') and (b = 'a') and (c = 'i121');
EXPLAIN
{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t1",
      "access_type": "range",
      "key": "idx_t1_1",
      "key_length": "163",
      "used_key_parts": ["a1", "a2", "b", "c"],
      "rows": 65,
      "filtered": 100,
      "attached_condition": "((t1.b = 'a') and (t1.c = 'i121') and (t1.a2 >= 'b'))",
      "using_index_for_group_by": "scanning"
    }
  }
}
drop table t1;