MySQL检查是否子查询返回NULL，然后替换值

我有MySQL查询，如果子查询返回没有结果或空值，我需要在WHERE子句中替换值。MySQL检查是否子查询返回NULL，然后替换值

价格查询其工作方式需要

成功运行

SELECT `prices` FROM `pricing` 
WHERE (3 BETWEEN `from_unit` AND `to_unit`) 
AND `type` = 1 
AND `id_pricing` IN 
    ( 
     SELECT v1.`id_pricing` FROM `values` AS v1 
     INNER JOIN `values` AS v2 ON v1.`id_pricing` = v2.`id_pricing` 
     INNER JOIN `values` AS v3 ON v1.`id_pricing` = v3.`id_pricing` 
     INNER JOIN `values` AS v4 ON v1.`id_pricing` = v4.`id_pricing` 
     WHERE v1.`id_attribute` = 1 AND v1.`id_value` = 1 
     AND v2.`id_attribute` = 7 AND v2.`id_value` = 63 
     AND v3.`id_attribute` = 8 AND v3.`id_value` = 87 
     AND v4.`id_attribute` = 12 AND v4.`id_value` = 143 
    )

当我如下修改此查询，在IN子句中的子查询添加IFNULL检查，它会引发错误

'SQL错误（1242）：子查询返回多于一行'

SELECT `prices` FROM `pricing` 
WHERE (3 BETWEEN `from_unit` AND `to_unit`) 
AND `type` = 1 
AND `id_pricing` IN 
    ( IFNULL (
        ( SELECT v1.`id_pricing` FROM `values` AS v1 
         INNER JOIN `values` AS v2 ON v1.`id_pricing` = v2.`id_pricing` 
         INNER JOIN `values` AS v3 ON v1.`id_pricing` = v3.`id_pricing` 
         INNER JOIN `values` AS v4 ON v1.`id_pricing` = v4.`id_pricing` 
         WHERE v1.`id_attribute` = 1 AND v1.`id_value` = 1 
         AND v2.`id_attribute` = 7 AND v2.`id_value` = 63 
         AND v3.`id_attribute` = 8 AND v3.`id_value` = 87 
         AND v4.`id_attribute` = 12 AND v4.`id_value` = 143 
        ), 
        '1234' 
       ) 
    )

我试着用COALESCE替换IFNULL的结果仍然相同。我使用错误的语法吗？

来源

2013-07-09 Abhishek Madhani

不'的'为什么SELECT IFNULL（v1.id_pricing， '1234'）子查询？ –

下面是一个解决方案的类似问题：http://stackoverflow.com/questions/9861171/how-to-resolve-this-in-mysql-1242-subquery-returns-more-than-1-row – Gimmy

我'被这个子查询混淆了。它应该做什么？考虑通过演示方式提供sqlfiddle – Strawberry

可能将其移动到LEFT JOIN和检查，要么存在记录的，或者说定价是1234 -

SELECT `prices` 
FROM `pricing` 
LEFT OUTER JOIN 
(
    SELECT v1.`id_pricing`, COUNT(*) 
    FROM `values` AS v1 
    INNER JOIN `values` AS v2 ON v1.`id_pricing` = v2.`id_pricing` 
    INNER JOIN `values` AS v3 ON v1.`id_pricing` = v3.`id_pricing` 
    INNER JOIN `values` AS v4 ON v1.`id_pricing` = v4.`id_pricing` 
    WHERE v1.`id_attribute` = 1 AND v1.`id_value` = 1 
    AND v2.`id_attribute` = 7 AND v2.`id_value` = 63 
    AND v3.`id_attribute` = 8 AND v3.`id_value` = 87 
    AND v4.`id_attribute` = 12 AND v4.`id_value` = 143 
    GROUP BY v1.`id_pricing` 
) Sub1 
ON Sub1.id_pricing = pricing.id_pricing 
WHERE (3 BETWEEN `from_unit` AND `to_unit`) 
AND `type` = 1 
AND (Sub1.`id_pricing` IS NOT NULL 
OR pricing.id_pricing = '1234')

来源

2013-07-09 08:17:03 Kickstart

MySQL检查是否子查询返回NULL，然后替换值

回答

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