Question

假设我有序列号，测试名称和其他一些列，我想为特定序列号编写TESTNAME is null条件，然后将TESTNAME设置为空，否则执行内连接

SELECT 
    (A.PTNUMBER + '-' +A.SL_NO) AS ENUMBER, 
    D.ENGINEER AS REQ, D.DATETIME as "DATE",
    (select Value 
     from DROPDOWN 
     where B.TEST_NAME=CONVERT(VARCHAR,DropdownID)) TESTNAME, 
    TABLE_NAME AS TABLETD 
FROM INSPECTION D 
INNER JOIN TABLEA A ON D.ENGID = CONVERT(VARCHAR,A.EN_ID) 
INNER JOIN TABLEB B ON B.ENGID = CONVERT(VARCHAR,A.EN_ID) 
INNER JOIN TABLEC C ON C.ENGID = CONVERT(VARCHAR,A.EN_ID)

Answer 1

不确定将testname设置为空白是什么意思，但如果您打算使用SELECT查询，那么您可以这样做

select *,
case when TESTNAME is null and serial_number = some_value then '' end as TESTNAME
from mytable

Answer 2

您可以将case表达式和coalesce()与您的联接结合使用，以选择要返回的值。

select serial_number, ... 
  ,case when coalesce(testname,'') <> ''
          then t2.testname 
        else coalesce(testname,'') end
from t
  inner join t2
    on ...

您可以在sql server中使用isnull()或coalesce()来返回不同的值来替换null。

select isnull(testname,'')

或

select coalesce(testname,'')

两者之间的主要区别在于coalesce()可以支持2个以上的参数，并选择第一个不是null的参数。两者之间的差异更大answered here.

select coalesce(testname,testname2,'')

coalesce()也是标准的ANSI sql，因此您可以在大多数RDBMS中找到它。 isnull()特定于sql server。

参考：

Answer 3

SELECT (A.PTNUMBER + '-' + A.SL_NO) AS ENUMBER, 
       D.ENGINEER AS REQ, 
       D.DATETIME as "DATE",
       case
        when SerialNo = xxx and TESTNAME is null then ''
        else (select Value from DROPDOWN where B.TEST_NAME = CONVERT(VARCHAR, DropdownID))
       end AS TESTNAME, 
       TABLE_NAME AS TABLETD 
  FROM INSPECTION D
  INNER JOIN TABLEA A ON D.ENGID = CONVERT(VARCHAR, A.EN_ID) 
  INNER JOIN TABLEB B ON B.ENGID = CONVERT(VARCHAR, A.EN_ID) 
  INNER JOIN TABLEC C ON C.ENGID = CONVERT(VARCHAR, A.EN_ID);

如果在MSSQL中有其他情况

3 个答案: