Question

我想在select query中应用以下条件。

IF  (TYPE = MBUSA or SDSA or MDSA OR PC) and (FINAL_STATUS = ACTIVE OR EXECUTED) 
then GET ID and Parent_ID
ELSEIF (TYPE = MSA) and (FINAL_STATUS = ACTIVE OR EXECUTED)
then  GET ID---(USING the ID from the else if condition AS FILTER, 
IF TYPE = (DSA OR BUSA) AND (FINAL_STATUS = ACTIVE OR EXECUTED) 
then GET ID and Parent_ID)

我是否需要编写程序？

以下是数据库结构：

Answer 1

CASE语句可以用作IF.. THEN... ELSE...语句的等效语句。不太确定你是如何选择它们的，因为你的问题不清楚，所以这里有一些建议。

使用条件格式的字符串表示选择单个列：

SELECT
    CASE
        WHEN (TYPE IN ('MBUSA','SDSA','MDSA','PC') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED')) 
            THEN ID + ' ' + P_ID
        WHEN ((TYPE = 'MSA') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED'))
            THEN ID
        WHEN (TYPE IN ('DSA','BUSA') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED')) 
            THEN ID + ' ' + P_ID
        ELSE ''
    END AS columnName
FROM
    tableName

将每个选择成单独的列

SELECT
    CASE
        WHEN (TYPE IN ('MBUSA','SDSA','MDSA','PC') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED')) 
            THEN ID
        WHEN ((TYPE = 'MSA') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED'))
            THEN ID
        WHEN (TYPE IN ('DSA','BUSA') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED')) 
            THEN ID
        ELSE ''
    END AS columnOneName
    CASE
        WHEN (TYPE IN ('MBUSA','SDSA','MDSA','PC') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED')) 
            THEN P_ID
        WHEN ((TYPE = 'MSA') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED'))
            THEN NULL
        WHEN (TYPE IN ('DSA','BUSA') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED')) 
            THEN  P_ID
        ELSE ''
    END AS columnTwoName
FROM
    tableName

虽然看上面的内容（我可能错误地转录了你的逻辑）但是当你可以逃脱2时有三种情况说明：

CASE
    WHEN (TYPE IN ('MBUSA','SDSA','MDSA','PC','DSA','BUSA') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED')) 
        THEN ID + ' ' + P_ID
    WHEN ((TYPE = 'MSA') AND (FINAL_STATUS IN ('ACTIVE','EXECUTED'))
        THEN ID
    ELSE ''
END AS columnName

我知道你现在已经放了一个截图，但SQL Fiddle可能会更有帮助或更详细，以便表名等可以很容易

有用的链接：

http://technet.microsoft.com/en-us/library/ms181765.aspx

SQL Case Statement Syntax?

http://blog.sqlauthority.com/2007/04/14/sql-server-case-statementexpression-examples-and-explanation/

Answer 2

您可以使用CASE在PL / SQL中实现IF-THEN-ELSE - 这只是一个例子：

    select case field1 WHEN '1' THEN 'VALUE1'
                       WHEN '2' THEN 'VALUE2'
                       ELSE 'VALUEOTHER'
                       END,
           case field2 WHEN '1' THEN 'VALUE1'
                       WHEN '2' THEN 'VALUE2'
                       ELSE 'VALUEOTHER'
                       END                  
    from (                   

    select '1' "FIELD1",
           '2' "FIELD2"
    from dual
    );

您不能在多列上使用CASE语句;但是，如果你需要比较在同一个CASE语句中的多个字段，您可以使用这样的解决方法：

    select case field1 || '_' || field2
                       WHEN '1_1' THEN 'FIELD1-IS-VALUE1 AND FIELD2-IS-VALUE1'
                       WHEN '1_2' THEN 'FIELD1-IS-VALUE1 AND FIELD2-IS-VALUE2'
                       WHEN '2_1' THEN 'FIELD1-IS-VALUE2 AND FIELD2-IS-VALUE1'
                       WHEN '2_2' THEN 'FIELD1-IS-VALUE2 AND FIELD2-IS-VALUE2'
                       ELSE 'VALUEOTHER'
                       END
    from (                   

    select '1' "FIELD1",
           '2' "FIELD2"
    from dual
    );

如果SQL语句变得难以阅读，最好使用带有SQL语句的视图或使用PL / SQL。

参考文献：

https://dba.stackexchange.com/questions/18239/using-same-case-when-conditions-for-multiple-query-columns

如何在选择查询中添加if-then-else条件？

2 个答案: