mysql 插入时带判断条件

INSERT INTO table (f1 ,f2 ,f3)
SELECT 1 ,'a',3 FROM DUAL WHERE NOT EXISTS
    (SELECT 1 FROM table2 where a = b)

DUAL 为临时表 ，也可以查找真实表字段插入。

需要插入多条数据时，可使用 UNION ：

INSERT INTO table (f1 ,f2 ,f3)
SELECT 1 ,'a',3 FROM DUAL WHERE NOT EXISTS
    (SELECT 1 FROM table2 where a = b)
UNION
SELECT 10 ,'ab',30 FROM DUAL WHERE NOT EXISTS
    (SELECT 1 FROM table2 where a = b)