Sergei Petrunia added a comment - 2015-04-10 18:41 An example that calls JOIN::make_simple_join() twice: create table t5 (a int , b int) ; create table t6 like t5 ; create table t7 like t5 ; insert into t5 values (0, 100), (1, 2), (1, 3), (2, 2), (2, 7), (2, -1), (3, 10) ; insert into t6 values (0, 0), (1, 1), (2, 1), (3, 1), (4, 1) ; insert into t7 values (3, 3), (2, 2), (1, 1) ; select count(distinct t5.b) as sum from t5, t6 where t5.a=t6.a and t6.b > 0 and t5.a <= 5 group by t5.a order by sum limit 1 This executes as follows: 1. create a tmp. table $TMP1 (without any keys) 2. run the join, put its output into $TMP1 3. create a temporary table $TMP2 (without any keys again) 4. use filesort() sort data from $TMP1 (produces an ordered stream) 5. read data from filesort result, do group-by-on-the-fly and write into $TMP2. // make_simple_join call. 6. use filesort(), read from $TMP2 and sort 7. read from filesort results and write to output.

Sergei Petrunia added a comment - 2015-04-12 13:32 MDEV-6995 has info about research done for EXPLAIN=JSON on this topic

Julien Fritsch added a comment - 2023-12-05 09:26 Automated message: ---------------------------- Since this issue has not been updated since 6 weeks, it's time to move it back to Stalled.