MySQL檢查是否子查詢返回NULL，然後替換值

我有MySQL查詢，如果子查詢返回沒有結果或空值，我需要在WHERE子句中替換值。MySQL檢查是否子查詢返回NULL，然後替換值

價格查詢其工作方式需要

成功運行

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 
    )

當我如下修改此查詢，在IN子句中的子查詢添加IFNULL檢查，它會引發錯誤

'SQL錯誤（1242）：子查詢返回多於一行'

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' 
       ) 
    )

我試着用COALESCE替換IFNULL的結果仍然相同。我使用錯誤的語法嗎？

來源

2013-07-09 Abhishek Madhani

不'的'爲什麼SELECT IFNULL（v1.id_pricing， '1234'）子查詢？ –

下面是一個解決方案的類似問題：http://stackoverflow.com/questions/9861171/how-to-resolve-this-in-mysql-1242-subquery-returns-more-than-1-row – Gimmy

我'被這個子查詢混淆了。它應該做什麼？考慮通過演示方式提供sqlfiddle – Strawberry

可能將其移動到LEFT JOIN和檢查，要麼存在記錄的，或者說定價是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')

來源

2013-07-09 08:17:03 Kickstart

MySQL檢查是否子查詢返回NULL，然後替換值

回答

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