Mysql 尽管主记录为空,左连接如何返回值?
我的SQL查询如下所示:Mysql 尽管主记录为空,左连接如何返回值?,mysql,Mysql,我的SQL查询如下所示: SELECT SUM(i.itemPrice) as total, t.sTax FROM items AS i LEFT JOIN tax_table AS t ON t.branchID = 10 WHERE i.orderID = 10 当订单ID 10的总计不是空时,它将返回sTax值。如果订单ID 10的总计为NULL,sTax为NULL 如果total为NULL,如何获取sTax?这里是您要查找的查询: SELECT SUM(i.itemPrice)
SELECT SUM(i.itemPrice) as total, t.sTax
FROM items AS i
LEFT JOIN tax_table AS t ON t.branchID = 10
WHERE i.orderID = 10
当订单ID 10的总计不是空时,它将返回sTax
值。如果订单ID 10的总计为NULL
,sTax
为NULL
如果total
为NULL
,如何获取sTax
?这里是您要查找的查询:
SELECT SUM(i.itemPrice) AS total
,CASE
WHEN SUM(i.itemPrice) IS NULL THEN (SELECT t.sTax
FROM tax_table AS t
WHERE t.branchID = 10
LIMIT 1)
ELSE NULL
END AS tax
FROM items AS i
WHERE i.orderID = 10
GROUP BY i.orderID
查询返回每个项目的总价,如果此总价为NULL
,则返回税费(否则税费为NULL
)
希望这会有所帮助