删除查询，其中表中的数据不存在于其他表中

Question

一个典型的删除表行的查询通常是这样的，对吧？

$query1 = odbc_exec($conn, "DELETE FROM table1 WHERE uname1 <> uname2");

但是，如果我想要uname2在另一个表中这样的方式怎么办？

Answer 1

DELETE FROM table1
WHERE uname1 NOT IN (
    SELECT uname2
    FROM table2
)

Answer 2

如果uname1是唯一的，则可以执行以下操作：

DELETE FROM table1 AS t1
WHERE uname1 NOT IN (
    SELECT uname2
    FROM table2 AS t2
    WHERE t2.uname1 = t1.uname1
);