Question

我有两个表Received和Issued，它们与ID字段有关。我试图使用以下查询来获取结果，它只在两个表都有值时才有效。但是当一个表为空时，查询返回NULL值。我需要帮助

SELECT 
    c.vaccine_id,
    c.name, 
    SUM(QRecived-IsuedQuan) Quantity 
FROM 
    vaccine c 
    LEFT OUTER JOIN (
        SELECT SUM(quantity_recieved) QRecived,vaccine_id from vaccine_detail group by vaccine_id
    ) a ON a.vaccine_id=c.vaccine_id 
    LEFT OUTER JOIN (
        select SUM(issued_quantity) IsuedQuan,vaccine_id from issued_item group by vaccine_id 
    ) b  ON b.vaccine_id=a.vaccine_id " 
GROUP BY c.vaccine_name,c.vaccine_id ";

注意：上面的查询将在SQLITE中运行，这只是为了通知您SQLLITE不支持RIGHT＆amp;完全加入

Answer 1

您不需要外部group by。问题是，当没有匹配时，值为NULL，因此您需要将其替换为其他值：

SELECT v.vaccine_id, v.name, 
       coalesce(r.QReceived, 0) - coalesce(i.IssuedQuan, 0) as Quantity 
FROM vaccine v LEFT OUTER JOIN
     (SELECT SUM(quantity_recieved) as QReceived, vaccine_id 
      FROM vaccine_detail  
      GROUP BY vaccine_id
     ) r
     ON r.vaccine_id = v.vaccine_id LEFT OUTER JOIN
     (SELECT SUM(issued_quantity) as IssuedQuan, vaccine_id 
      FROM issued_item 
      GROUP BY vaccine_id 
     ) i
     ON i.vaccine_id = v.vaccine_id;

您可以使用isnull()或coalesce()，但coalesce()是ANSI标准功能。

Answer 2

SELECT c.vaccine_id,
       c.name,
       SUM(IfNull(QRecived,0) - IfNull(IsuedQuan,0)) Quantity
FROM vaccine c
....

应该照顾好。

SQL查询：从不同的表中汇总两个不同的列

2 个答案: