drop table if exists t; create table t (id int, c1 timestamp); show columns from t; explain t; describe t; desc t; desc t c1; desc t id; drop table if exists t; create table t(id int primary key, a int, b int); set session tidb_hashagg_partial_concurrency = 1; set session tidb_hashagg_final_concurrency = 1; explain select group_concat(a) from t group by id; explain select group_concat(a, b) from t group by id; drop table t; drop view if exists v; create view v as select cast(replace(substring_index(substring_index("",',',1),':',-1),'"','') as CHAR(32)) as event_id; desc v;