Question

我有这个select语句，它运行一个标题为＆＃39; product_id＆＃39;和一个价值。

SELECT meta_value as product_id
FROM ctc_woocommerce_order_itemmeta
LEFT JOIN ctc_woocommerce_order_items ON ctc_woocommerce_order_itemmeta.order_item_id = ctc_woocommerce_order_items.order_item_id
WHERE meta_key = '_product_id'
AND order_id = 3988

我希望结果与此声明相结合：

SELECT meta_value as variation_id
FROM ctc_woocommerce_order_itemmeta
LEFT JOIN ctc_woocommerce_order_items ON ctc_woocommerce_order_itemmeta.order_item_id = ctc_woocommerce_order_items.order_item_id
WHERE meta_key = '_variation_id'
AND order_id = 3988

如何结合2？我试过UNION，也试过类似的声明，但是phpMyAdmin崩溃了。

SELECT x.a, y.b FROM (SELECT * from a) as x, (SELECT * FROM b) as y

我正在寻找带有2列的输出：

1 x product_id

1 x variation_id

Answer 1

我认为你在错误的地方写了SELECT。

SELECT (
  SELECT meta_value as product_id
  FROM ctc_woocommerce_order_itemmeta
  LEFT JOIN ctc_woocommerce_order_items ON ctc_woocommerce_order_itemmeta.order_item_id = ctc_woocommerce_order_items.order_item_id
  WHERE meta_key = '_product_id'
  AND order_id = 3988
) as product_id,
(
  SELECT meta_value as variation_id
  FROM ctc_woocommerce_order_itemmeta
  LEFT JOIN ctc_woocommerce_order_items ON ctc_woocommerce_order_itemmeta.order_item_id = ctc_woocommerce_order_items.order_item_id
  WHERE meta_key = '_variation_id'
  AND order_id = 3988
) as variation_id;

Answer 2

尝试使用子查询加入：

SELECT t1.meta_value as product_id, sub1.variation_id AS variation_id
FROM ctc_woocommerce_order_itemmeta t1
LEFT JOIN ctc_woocommerce_order_items ON 
ctc_woocommerce_order_itemmeta.order_item_id = 
ctc_woocommerce_order_items.order_item_id

JOIN

    (SELECT meta_key, order_id, meta_value as variation_id
        FROM ctc_woocommerce_order_itemmeta
        LEFT JOIN ctc_woocommerce_order_items ON 
        ctc_woocommerce_order_itemmeta.order_item_id = 
        ctc_woocommerce_order_items.order_item_id
    ) AS sub1

WHERE t1.meta_key = '_product_id' AND t1.order_id = 3988
AND sub1.meta_key = '_variation_id' AND sub1.order_id = 3988

Answer 3

我尝试将子查询中的两个id字段排序，然后将其连接到订单行表。

另外，当你在一个表中的一个字段上添加一个WHERE条件时，它就是OUTER JOINing，它就变成了一个INNER JOIN，无论如何我觉得这真的是你想要的。为了便于阅读，我添加了表别名。

可能有一种更优雅的方式从该子查询中获取id字段，但是如果没有样本数据，我使用的方法我非常肯定会起作用。但是，自联接可能会更高效。

SELECT
  im.product_id,
  im.variation_id
FROM
  (
    SELECT
      order_item_id,
      MAX(CASE WHEN meta_key = '_product_id' THEN meta_value ELSE '' END) AS product_id,
      MAX(CASE WHEN meta_key = '_variation_id' THEN meta_value ELSE '' END) AS variation_id
    FROM
      ctc_woocommerce_order_itemmeta
  ) AS im
INNER JOIN 
  ctc_woocommerce_order_items AS oi 
    ON im.order_item_id = oi.order_item_id
    AND
    oi.order_id = 3988

Answer 4

在我看来，您甚至不需要LEFT JOIN和ctc_woocommerce_order_items表。由于ctc_woocommerce_order_items表中不需要任何字段。同样使用table_A LEFT JOIN table_B，这意味着无论table_B中是否存在匹配记录，始终从table_A返回记录。所以我在这里简化它：

SELECT
    a.product_id,
    b.variation_id
FROM
(
    SELECT
        order_id,
        meta_value as product_id
    FROM
        ctc_woocommerce_order_itemmeta
    WHERE
        meta_key = '_product_id'
        AND order_id = 3988
    LIMIT 1
) a

JOIN

(
    SELECT
        order_id,
        meta_value as variation_id
    FROM
        ctc_woocommerce_order_itemmeta
    WHERE
        meta_key = '_variation_id'
        AND order_id = 3988
    LIMIT 1
) b

ON a.order_id = b.order_id;

组合2个SELECT LEFT JOIN查询，联合/声明AS不起作用

4 个答案: