如何通过选择插入时插入表格之前如何检查重复项：
insert into table1 select col1,col2 from table2
我需要检查table1是否已经有一行table1.col1.value = table2.col1.value,如果是,则从插入中排除该行.
解决方法
INSERT INTO table1
SELECT t2.col1,t2.col2
FROM table2 t2
LEFT JOIN table1 t1
ON t2.col1 = t1.col1
AND t2.col2 = t1.col2
WHERE t1.col1 IS NULL
替代使用除外
INSERT INTO @table2
SELECT col1,col2
FROM table1
EXCEPT
SELECT t1.col1,t1.col2
FROM table1 t1
INNER JOIN table2 t2
ON t1.col1 = t2.col1
AND t1.col2 = t2.col2
替代使用不存在
INSERT INTO table2
SELECT col1,col2
FROM table1 t1
WHERE
NOT EXISTS( SELECT 1
FROM table2 t2
WHERE t1.col1 = t2.col1
AND t1.col2 = t2.col2)
