在 SQL 中使用 IN 运算符

Question

Suppose I have the database consisting of T1 (a, b, c) And I also have the database T2 (a, b, c) Can I use the IN operator to check that there is a record from T1 to T2? Like this for example:

select a
from T1
where (a, b, c) in (select a, b, c
                    from T2)

Or does the IN operator only work on a single value? Thanks for answering:)

Answer 1

It depends on your database. Some databases (MySQL, Postgres, Oracle, for instance) support tuples with in . Others do not (SQL Server).

All databases can use exists :

select a
from T1
where exists (select 1
              from t2
              where t2.a = t1.a and t2.b = t1.b and t2.c = t1.c
             );

Answer 2

Your query can be rewritten using exists

select a
from T1 t1
where exists (select 1
                    from T2 t2 t1.a = t2.a and t1.b = t2.b and t1.c = t2.c)