db2，with 子句、变量和多重连接

Question

我只是不知道如何使用创建和使用变量的好技术，如下例所示：

WITH t(myvar) AS (VALUES('welcome'))
SELECT tablename.*
FROM   tablename, t
WHERE  tablename.column1 = t.myvar

在这样的多连接查询中：

WITH t(myvar) AS (VALUES('welcomeagain'))
SELECT 
    tablename.*,
    joinedtable.valueid
FROM   
    tablename, t?
    left join joinedtable on
    joinedtable.keyid = tablename.keyid
WHERE  
    tablename.column1 = t.myvar

我的意思是，我必须在哪里、如何以及到什么地方加入“t”？环境是 DB2 ISeries 7.2。

非常感谢您的帮助

马丁

Answer 1

也许这就是你想要的？

WITH t(myvar) AS (VALUES('welcomeagain'))
SELECT 
    tablename.*,
    t.myvar, 
    joinedtable.valueid
FROM   
    tablename
    join t on tablename.column1 = t.myvar
    left join joinedtable on joinedtable.keyid = tablename.keyid

或者这个

WITH t(myvar) AS (VALUES('welcomeagain'))
SELECT 
    tablename.*,
    t.myvar, 
    joinedtable.valueid
FROM   
    tablename
    left join t on tablename.column1 = t.myvar
    left join joinedtable on joinedtable.keyid = tablename.keyid

或者这个

WITH t(myvar) AS (VALUES('welcomeagain'))
SELECT 
    tablename.*,
    t.myvar, 
    joinedtable.valueid
FROM   
    tablename
    cross join t 
    left join joinedtable on joinedtable.keyid = tablename.keyid

你不想要的是逗号——因为这是一种旧式连接，并且将它与新式连接结合起来的语法总是有点迟钝（如果它确实有效的话。）