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)
原文：https://www.cnblogs.com/qingyibusi/p/9176937.html