在mysql中使用UNION时无法排序

Question

如果我不做 UNION，我的这个查询就可以工作：

SELECT t1.offer_id, t1.cpv_id, t1.type,
FROM `offer_cpv` t1
JOIN `offer` t2     ON t1.offer_id = t2.id
JOIN `company` t3   ON t2.cmpid = t3.id
WHERE t1.cpv_id = :cpvid
AND t3.status IN (4, 6)
GROUP BY t1.offer_id
ORDER BY t1.type

关键部分是我在做ORDER BY t1.type。但是，如果我使用 UNION（而且我必须），我的查询会中断：

“订单子句”中的未知列“t1.type”

以下是我的 UNION 尝试不起作用：

SELECT t1.offer_id, t1.cpv_id, t1.type,
FROM `offer_cpv` t1
JOIN `offer` t2    ON t1.offer_id = t2.id
JOIN `company` t3  ON t2.cmpid = t3.id
WHERE t1.cpv_id = :cpvid
AND t3.status IN (4, 6)
GROUP BY t1.offer_id
ORDER BY t1.type

UNION

SELECT t1.offer_id, t1.cpv_id, t1.type,
FROM `offer_cpv` t1
JOIN `offer` t2      ON t1.offer_id = t2.id
JOIN `company_2` t3  ON t2.cmpid = t3.id
WHERE t1.cpv_id = :cpvid
AND t3.status IN (4, 6)
GROUP BY t1.offer_id

ORDER BY t1.type

还有：

SELECT t1.offer_id, t1.cpv_id, t1.type,
FROM `offer_cpv` t1
JOIN `offer` t2    ON t1.offer_id = t2.id
JOIN `company` t3  ON t2.cmpid = t3.id
WHERE t1.cpv_id = :cpvid
AND t3.status IN (4, 6)
GROUP BY t1.offer_id

UNION

SELECT t1.offer_id, t1.cpv_id, t1.type,
FROM `offer_cpv` t1
JOIN `offer` t2      ON t1.offer_id = t2.id
JOIN `company_2` t3  ON t2.cmpid = t3.id
WHERE t1.cpv_id = :cpvid
AND t3.status IN (4, 6)
GROUP BY t1.offer_id

ORDER BY t1.type

我能否以某种方式执行此 UNION 但按类型排序结果。我按类型订购，因为我需要得到这样的输出：

<h2> Results of type 1 from both tables: </h2>
<div> Result 1 from **first** table </div>
<div> Result 2 from first table </div>
<div> Result 1 from **second** table </div>
<div> Result 2 from second table </div>
<h2> Results of type 2 from both tables: </h2>
<div> Result 1 from **first** table </div>
<div> Result 2 from first table </div>
<div> Result 1 from **second** table </div>
<div> Result 2 from second table </div>

稍后我将不得不在 ORDER BY 子句中再添加一列：t1.rank，这样我就可以先按类型排序，然后也按排名！

Answer 1

来自MySQL manual：

这种 ORDER BY 不能使用包含 表名（即 tbl_name.col_name 格式的名称）。反而， 在第一个 SELECT 语句中提供一个列别名并参考 ORDER BY 中的别名。 （或者，请参阅 ORDER BY 使用其列位置。但是，使用列位置 已弃用。）

所以基本上你需要 (i) 为需要在 first 查询中排序的列创建别名 (ii) 在 ORDER BY 子句中使用别名：

SELECT t1.offer_id, t1.cpv_id, t1.type AS type_column --, t1.rank as rank_column
FROM `offer_cpv` t1
JOIN `offer` t2 ON t1.offer_id = t2.id
JOIN `company` t3 ON t2.cmpid = t3.id
WHERE t1.cpv_id = :cpvid AND t3.status IN (4, 6)
GROUP BY t1.offer_id

UNION

SELECT t1.offer_id, t1.cpv_id, t1.type --, t1.rank
FROM `offer_cpv` t1
JOIN `offer` t2 ON t1.offer_id = t2.id
JOIN `company_2` t3 ON t2.cmpid = t3.id
WHERE t1.cpv_id = :cpvid AND t3.status IN (4, 6)
GROUP BY t1.offer_id

ORDER BY type_column --, rank_column

Answer 2

您只能订购整个UNION。删除第一个 ORDER BY 别名都 t1.type 到别的东西，比如“mytype”。然后把第二个ORDER BY改成ORDER BY mytype。

看这里：

SQL Query - Using Order By in UNION