Question

我遇到需要从两个表中检索结果的情况。表A名为'MEMBERS'，表B名为'MEMBERUDFS'。我需要对表进行LEFT JOIN，因为'MEMBERS'中的所有行都不会在'MEMBERUDFS'中有一个条目。我需要从'MEMBERS'中提取符合条件的行和来自'MEMBERUDFS'的行（不是MEMBERUDFS中的所有条目都与此查询相关）。这是我需要相同帮助的地方：我当前的查询返回MEMBERS表中的所有字段以及MEMBERUDFS中的相应行，从而为每个成员返回多行。我想要做的是让MEMBERUDFS表中的字段与MEMBERS数据在同一行返回。例如，我得到：

lastname   firstname   relationship   email              entrydate   scancode   sitename   udflabel   udfvalue   expr1   expr2
doe        jane        p              janedoe@gmail.com  1/1/2016    1234       Home       Guest Pass Yes        steve   holmes
doe        jane        p              janedoe@gmail.com  1/1/2016    1234       Home       Pass Used  No         steve   holmes
doe        jane        p              janedoe@gmail.com  1/1/2016    1234       Home       Visited    yes        steve   holmes

我正在寻找的是：

doe   jane  p  janedoe@gmail.com  1/1/2016    1234   Guest Pass    Yes    steve    holmes     Pass Used     No     Visited     yes

以下是我的疑问：

SELECT MEMBERS.lname, MEMBERS.fname, MEMBERS.relationship, MEMBERS.email, MEMBERS.entrydate,
       MEMBERS.scancode, MEMBERS.siteid, SITES.sitename, 
       MEMBERUDFSETUPS.udflabel, MEMBERUDFS.udfvalue, EMPLOYEES.lname AS Expr1,
       EMPLOYEES.fname AS Expr2
FROM MEMBERS
  LEFT OUTER JOIN MEMBERUDFS ON MEMBERS.memid = MEMBERUDFS.memid
  INNER JOIN MEMBERUDFSETUPS ON MEMBERUDFS.udfid = MEMBERUDFSETUPS.udfid
  INNER JOIN SITES ON MEMBERS.siteid = SITES.siteid
  INNER JOIN EMPLOYEES ON MEMBERS.employeeid = EMPLOYEES.employeeid
WHERE (MEMBERS.relationship = 'P')
  AND (MEMBERS.siteid = @rvSite)
  AND (MEMBERUDFS.udfid = '25' OR
       MEMBERUDFS.udfid = '26' OR
       MEMBERUDFS.udfid = '27')
  AND (MEMBERS.entrydate BETWEEN @entryDateStart AND @entryDateEnd)
ORDER BY MEMBERS.entrydate DESC

Answer 1

您可以采取两种方法。最简单的方法是多次加入MEMBERUDFS表，对于您要检索的每个udfid一次。下面是一小段示例代码。

SELECT
    MEMBERS.lname
    ,MEMBERS.fname
    ,MEMBERS.relationship
    ,MEMBERS.email
    ,MEMBERS.entrydate
    ,MEMBERS.scancode
    ,MEMBERS.siteid
    ,SITES.sitename
    ,MUS_25.udflabel
    ,MU_25.udfvalue
    ,MUS_26.udflabel
    ,MU_26.udfvalue
    ,MUS_27.udflabel
    ,MU_27.udfvalue
    ,EMPLOYEES.lname AS Expr1
    ,EMPLOYEES.fname AS Expr2
FROM
    MEMBERS
    LEFT OUTER JOIN MEMBERUDFS MU_25
        ON MEMBERS.memid = MU_25.memid AND
            MU_25.udfid = '25'
    LEFT OUTER JOIN MEMBERUDFSETUPS MUS_25
        ON MU_25.udfid = MUS_25.udfid
    LEFT OUTER JOIN MEMBERUDFS MU_26
        ON MEMBERS.memid = MU_26.memid AND
            MU_26.udfid = '26'
    LEFT OUTER JOIN MEMBERUDFSETUPS MUS_26
        ON MU_26.udfid = MUS_26.udfid
    LEFT OUTER JOIN MEMBERUDFS MU_27
        ON MEMBERS.memid = MU_27.memid AND
            MU_27.udfid = '27'
    LEFT OUTER JOIN MEMBERUDFSETUPS MUS_27
        ON MU_27.udfid = MUS_27.udfid
    INNER JOIN SITES
        ON MEMBERS.siteid = SITES.siteid
    INNER JOIN EMPLOYEES
        ON MEMBERS.employeeid = EMPLOYEES.employeeid
WHERE
    (MEMBERS.relationship = 'P') AND
    (MEMBERS.siteid = @rvSite) AND
    (MEMBERS.entrydate BETWEEN @entryDateStart AND @entryDateEnd)
ORDER BY
    MEMBERS.entrydate DESC

请注意，如果您的udfid一致（始终使用相同的标签），则可以使用相应的标签为每个udfvalue添加别名：

SELECT
    MEMBERS.lname
    ,MEMBERS.fname
    ,MEMBERS.relationship
    ,MEMBERS.email
    ,MEMBERS.entrydate
    ,MEMBERS.scancode
    ,MEMBERS.siteid
    ,SITES.sitename
    ,MU_25.udfvalue AS Guest_Pass
    ,MU_26.udfvalue AS Pass_Used
    ,MU_27.udfvalue AS Visited
    ,EMPLOYEES.lname AS Expr1
    ,EMPLOYEES.fname AS Expr2
FROM
    MEMBERS
    LEFT OUTER JOIN MEMBERUDFS MU_25
        ON MEMBERS.memid = MU_25.memid AND
            MU_25.udfid = '25'
    LEFT OUTER JOIN MEMBERUDFS MU_26
        ON MEMBERS.memid = MU_26.memid AND
            MU_26.udfid = '26'
    LEFT OUTER JOIN MEMBERUDFS MU_27
        ON MEMBERS.memid = MU_27.memid AND
            MU_27.udfid = '27'
    INNER JOIN SITES
        ON MEMBERS.siteid = SITES.siteid
    INNER JOIN EMPLOYEES
        ON MEMBERS.employeeid = EMPLOYEES.employeeid
WHERE
    (MEMBERS.relationship = 'P') AND
    (MEMBERS.siteid = @rvSite) AND
    (MEMBERS.entrydate BETWEEN @entryDateStart AND @entryDateEnd)
ORDER BY
    MEMBERS.entrydate DESC

Answer 2

您想要做的事情通常称为 pivoting ：将行转换为列。它使用case语句完成。你没有给出UDFS表的清晰描述以及你想要它如何布局，但我可以告诉你如何去做，

select lname, fname 
       , max( case udfid when 25 then 'foo' end ) as col1
       , max( case udfid when 26 then 'foo' end ) as col2
from MEMBERS left join MEMBERUDFS 
...
group by lname, fname

某些DBMS具有PIVOT运算符，可以使查询更简洁或更高效地执行。如果要搜索示例，您应该找到＆＃34; fold＆＃34;和＆＃34;枢轴＆＃34;一起讨论。

SQL逻辑 - 两个表，表2中的多行

2 个答案: