替代表达式

返回单值（与 IN 子查询返回的值列表不同）的子查询可用于在 SQL 中允许使用表达式的任何位置。它可以是列名称、常数、函数、标量子查询或由运算符或子查询连接的列名称、常数和函数的组合。

例如：

=> SELECT c1 FROM t1 WHERE c1 = ANY (SELECT c1 FROM t2) ORDER BY c1;
=> SELECT c1 FROM t1 WHERE COALESCE((t1.c1 > ANY (SELECT c1 FROM t2)), TRUE);
=> SELECT c1 FROM t1 GROUP BY c1 HAVING
     COALESCE((t1.c1 <> ALL (SELECT c1 FROM t2)), TRUE);

多列表达式也受支持：

=> SELECT c1 FROM t1 WHERE (t1.c1, t1.c2) = ALL (SELECT c1, c2 FROM t2);
=> SELECT c1 FROM t1 WHERE (t1.c1, t1.c2) <> ANY (SELECT c1, c2 FROM t2);

如果用作表达式的任何子查询返回了一个以上的行，则 Vertica 将返回查询错误：

=> SELECT c1 FROM t1 WHERE c1 = (SELECT c1 FROM t2) ORDER BY c1;
   ERROR:  more than one row returned by a subquery used as an expression

另请参阅