Question

我通过连接获得了以下查询：

SELECT i.PropertyCodeId, i.IndividualCode, i.LastName, 
       i.Firstname, i.AccountCode, acc.Name AS AccountName,
       (SELECT value 
        FROM Relation.ContactDetail AS cd 
        WHERE cd.ContactDetailTypeCode = 'EMAIL' 
              AND cd.RelationCode = i.IndividualCode) AS Email,
       adr.City, adr.ZipCode, adr.StateCode, adr.CountryCode, 
       'undefined' AS MemberShipID, i.TierCode AS MemberShipTier,
       i.VipCode, i.Active, i.PrimaryRoleCode
FROM Relation.Individual AS i
    INNER JOIN Relation.Account AS acc ON i.AccountCode = acc.AccountNumber
    LEFT OUTER JOIN Relation.ContactDetail AS cd ON i.IndividualCode = cd.RelationCode
    INNER JOIN Relation.Address AS adr ON i.IndividualCode = adr.RelationCode

我的问题是关于这个陈述：

(SELECT value FROM Relation.ContactDetail AS cd WHERE cd.ContactDetailTypeCode = 'EMAIL' AND cd.RelationCode = i.IndividualCode) AS Email,

运行此语句将产生1行，但在大查询中运行它会产生4行，它还会显示不是EMAIL的ContactTypes的记录。

有谁知道我做错了什么？：（

Answer 1

select之后的列中的子查询对返回的行数没有影响。如果用'hello'替换子查询，您将看到查询仍然返回4行。

查找join语句中四行的原因。您通常可以逐个省略连接以找到罪魁祸首。

Answer 2

您正在执行子查询的同一个表上执行左连接，但左连接条件缺少限制：cd.ContactDetailTypeCode ='EMAIL'

添加此项可能会解决您的问题。也许您也可以删除子查询，只需直接从联接表中选择值

SELECT i.PropertyCodeId, i.IndividualCode, i.LastName, 
   i.Firstname, i.AccountCode, acc.Name AS AccountName,
   cd.value AS Email,
   adr.City, adr.ZipCode, adr.StateCode, adr.CountryCode, 
   'undefined' AS MemberShipID, i.TierCode AS MemberShipTier,
   i.VipCode, i.Active, i.PrimaryRoleCode
FROM Relation.Individual AS i
INNER JOIN Relation.Account AS acc ON i.AccountCode = acc.AccountNumber
LEFT OUTER JOIN Relation.ContactDetail AS cd ON (i.IndividualCode = cd.RelationCode AND cd.ContactDetailTypeCode = 'EMAIL')
INNER JOIN Relation.Address AS adr ON i.IndividualCode = adr.RelationCode

Answer 3

如果您的LEFT OUTER JOIN返回的行多于一行，则基本表（Relation.Individual）中的行会成倍增加。

Answer 4

运行此语句将产生1行，但在大查询中运行它会产生4行，它还会显示不是EMAIL的ContactTypes 的记录。

也许可能是因为你在错误的地方做了LEFT OUTER JOIN，或者LEFT OUTER JOIN应该是INNER JOIN。

如果您使用LEFT JOIN注意LEFT JOIN两侧的哪个表，因为左侧表的所有行都将位于结果集中。也许你应该将LEFT JOIN设置为第一个。

SQL多行但只有一行

4 个答案: