通过select插入表前如何检查重复项目？
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 WHEREt1.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)
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