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--source include/have_sequence.inc # Embedded doesn't have optimizer trace: --source include/not_embedded.inc create table t1 (a int, b int, c int); insert into t1 select seq,seq/2, seq/4 from seq_1_to_100; create table t2 (a int, b int, c int); insert into t2 select seq, seq/2, seq/4 from seq_1_to_200; analyze table t1,t2 persistent for all; set optimizer_trace=1; set join_cache_level=6; set optimizer_switch='hash_join_cardinality=on'; explain select * from t1, t2 where t1.a=t2.a and t1.a=t2.b and t1.c=t2.c; set @json= (select trace from information_schema.optimizer_trace); select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS; select json_detailed(json_extract(@json, '$**.rest_of_plan[*].rows_for_plan')) as ROWS_FOR_PLAN; explain select * from t1, t2 where t1.c=t2.c; set @json= (select trace from information_schema.optimizer_trace); select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS; select json_detailed(json_extract(@json, '$**.rest_of_plan[*].rows_for_plan')) as ROWS_FOR_PLAN; explain select * from t1 straight_join t2 where t1.c=t2.c and t2.a<30; set @json= (select trace from information_schema.optimizer_trace); --echo # Note that rows is the same: select json_detailed(json_extract(@json, '$**.hash_join_cardinality')) as JS; --echo # Despite available selectivity: select json_detailed(json_extract(@json, '$**.selectivity_for_columns')) as JS; drop table t1,t2;