drop table if exists t0, t1; 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 for 2*1000*1000*1000; ERROR HY000: Unknown thread id: 2000000000 show explain for (select max(a) from t0); ERROR 42000: This version of MySQL doesn't yet support 'Usage of subqueries or stored function calls as part of this statement' show explain for $thr2; ERROR HY000: Error when executing command SHOW EXPLAIN: Target is not running EXPLAINable command show explain for $thr1; ERROR HY000: Error when executing command SHOW EXPLAIN: Target is not running EXPLAINable command set @show_explain_probe_select_id=1; set debug='d,show_explain_probe_1'; select count(*) from t1 where a < 100000; show explain for $thr2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index a a 5 NULL 1000 Using where; Using index count(*) 1000 select max(c) from t1 where a < 10; show explain for $thr2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 range a a 5 NULL 10 Using where max(c) 9 set optimizer_switch='index_condition_pushdown=on,mrr=on,mrr_sort_keys=on'; explain select max(c) from t1 where a < 10; show explain for $thr2; 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 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 drop table t0,t1;