SQL Server null值带有内在连接
-
25-10-2019 - |
题
我正在使用C#和SQL Server。
看看以下SQL:
SELECT table1.id, table1.description, table2.name, table2.surname
FROM table1
INNER JOIN table2 ON table1.EmpID = table2.EmpID
它很简单,正常工作。它从Table1表中检索数据,并且内在连接 table1.empid
至 table2.name
和 table2.surname
正确。
现在,有时 table1.empid
为null,当它为null时,此SQL只是忽略了带有空值的“行”。根据标准,这是很正常的基础。
我在这里需要的是,还要以零值以及何时获得“行” table1.empid
null我需要将自定义值设置为 table2.name
和 table2.surname
.
我一直在和isnull()一起玩,但我所做的就是使它甚至更糟糕。
有什么建议么?
谢谢
解决方案
您需要做一个左联接:
SELECT table1.id, table1.description, table2.name, table2.surname FROM table1
LEFT JOIN table2 ON table1.EmpID = table2.EmpID;
其他提示
尝试使用联盟:
SELECT table1.id, table1.description, table2.name, table2.surname
FROM table1
INNER JOIN table2 ON table1.EmpID = table2.EmpID
UNION
SELECT table1.id, table1.description, 'Table 2 Null', 'Table 2 Null'
FROM table1
WHERE table1.empId is null
如果表1为null,并且您仍然需要无法开始的记录。从table2开始,然后加入table1。
SELECT table1.id, table1.description, ISNULL(table1.empid, "some new value") AS name, table2.surname
FROM table2
LEFT OUTER JOIN table1 ON table2.EmpID = table1.EmpID
SELECT table1.id
,table1.description
,COALESCE(table2.name, 'DEFAULT') AS name
,COALESCE(table2.surname, 'DEFAULT') AS surname
FROM table1
LEFT JOIN table2
ON table1.EmpID = table2.EmpID
现在请注意,当empid不是零的时候,这也将包括人,但是如果他们在表1中有empid,则“无效”,但在Table2中找不到,因此,如果您想避免使用,那么另一个选择是此选择:
SELECT table1.id
,table1.description
,table2.name
,table2.surname
FROM table1
INNER JOIN table2
ON table1.EmpID = table2.EmpID
UNION ALL
SELECT table1.id
,table1.description
,'DEFAULT' AS name
,'DEFAULT' AS surname
FROM table1
WHERE table1.EmpID IS NULL
Select table1.id table1.description
, Case When table1.EmpID Is Null Then 'Some Value' Else table2.name End As Table2Name
, Case When table1.EmpID Is Null Then 'Some Value' Else table2.surname End As Table2Surname
From table1
Left Join table2
On table2.EmpID = table1.EmpID
Where table1.EmpID Is Null
Or table2.EmpID Is Not Null
不隶属于 StackOverflow