MySQL；一列中有不同的ID？

非常感谢您的帮助

我现在正在使用这个查询

SELECT t.itemID, RepID, InsRepairID
    FROM tbl_item t
        left join tbl_insiderepair i on i.itemID = t.itemID
        left join tbl_underrepair u on u.itemID = t.itemID
    where(i.itemID = t.itemID Or u.itemID = t.itemID);

这就是结果

itemID     |     RepID     |     InsRepairID
1                       3                     null
2                      null                    1
3                      null                    2

现在我想将“RepID和insrepaiid列”（它们是来自不同表的ID）合并为一列。

您可以使用sql函数，如下所示：

SELECT t.itemID, IFNULL(RepID, InsRepairID) ID
FROM tbl_item t
left join tbl_insiderepair i on i.itemID = t.itemID
left join tbl_underrepair u on u.itemID = t.itemID

---

通过使用Union，可以在一列中添加两个表

Select  itemID, RepID from  tbl_item
union
SELECT   itemID,InsRepairID from tbl_insiderepair

SELECT t.itemID, COALESCE(RepID, InsRepairID)
    FROM tbl_item t
        left join tbl_insiderepair i on i.itemID = t.itemID
        left join tbl_underrepair u on u.itemID = t.itemID
    where(i.itemID = t.itemID Or u.itemID = t.itemID);