说我有一个查询,例如：
SELECT *
FROM Table_1
JOIN Table_2
ON Table_1.Col_1 = Table_2.Col_1
SELECT *
FROM Table_1
LEFT JOIN Table_2 ON (Table_1.Col_1 = Table_2.Col_1)
Table_2的字段将为NULL,其中ON子句不匹配.然后,您将能够添加WHERE TABLE_2.Col_1 IS NULL,以仅保留Table_1中没有Table_2匹配的记录.