MySQL检查子查询是否返回NULL，然后替换值

Question

我有一个 mysql 查询，如果子查询没有返回结果或空值，我需要替换 WHERE 子句中的值。

按需查询价格

运行成功

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时，在 IN 子句中对子查询添加 IFNULL 检查时，它会抛出错误

'SQL 错误 (1242):子查询返回超过 1 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'
                )
    )

我尝试用 COALESCE 替换 IFNULL 仍然是相同的结果。我是否使用了错误的语法。

Answer 1

可能将其移动到 LEFT JOIN 并检查是否有记录，或者定价是否为 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')