Alibabacloud, Database, Query Optimization, Sql, Relational Databases.
COUNT (*) From t2 Where t1.c1 = t2.c1 ) Distributed LeftMarkJoin LeftMarkJoin[2] in the paper Unnesting Arbitrary Queries[1] is also error-prone. Its output is the same as the semantics of the in clause. That is, its output is as follows. select t1.c1 in ( select t2.c1 from t2) from t1 The logic