通过select插入表前如何检查重复项目？

若依

通过select插入表前如何检查重复项：
insert into table1select col1,col2 from table2我需要检查table是否已有table1.col1.value = table2.col1.value如果是，从插入中排除行。

解决方案:
                                                            INSERT INTO table1 SELECT t2.col       t2.col2 FROM table2 t2       LEFT JOIN table1 t1                                                                                                                                                                                                                                                                                                                                                                            ON t2.col1 = t1.col1                                                                                                                                                                                                                                                                                                                                                                               AND t2.col2 = t1.col2 WHERE  t1.col1 IS NULL替代使用
INSERT INTO @table2 SELECT col       col2 FROM table1 EXCEPT SELECT t1.col       t1.col2 FROM table1 t1       INNER JOIN table2 t2                      ON t1.col1 = t2.col1          AND t1.col2 = t2.col2使用不存在的替代方法
INSERT INTO table2 SELECT col1,col2 FROM table1 t1WHERENOT EXISTS( SELECT 1 FROM table2 t2 WHERE t1.col1 = t2.col1                                                                                                                                                                                                                                                                                                                                                                            AND t1.col2 = t2.col2)

通过select插入表前如何检查重复项目？

若依 LV1