Question

假设我有这四张桌子。

PEOPOLE

ID NAME     SURNAME  COMPANY   UNIT   GROUPS
--------------------------------------------   
1  Michael  Backer      1        1      1
2  Travis   Morgan      2        2      2 
3  George   Marshall    3        3      3

COMPANY

ID NAME
------------
1  Coca Cola
2  Pepsi
3  Sprite

工作单元

ID NAME
-------------    
1  Finances
2  Marketing
3  Sales

组（两个值都可以为空）

ID NAME          FLOOR
-------------------------  
 1 Risks           5
 2 NULL           NULL
 3 Secretariat    NULL

预期结果

NAME SURNAME COMPANYNAME WORKUNIT GROUPS FLOOR
-----------------------------------------------    
Michael Backer Coca Cola Finances  Risks  5
Travis  Morgan Pepsi Marketing NULL NULL
George Marshall Sprite Sales Secretariat NULL

到目前为止，我写这个查询没有成功：

SELECT
    people.NAME, people.SURNAME, company.NAME,
    workunit.NAME, groups.NAME, groups.FLOOR
FROM
    company, workunit, groups, people
LEFT JOIN
    groups on people.GROUP = GROUPS.id
WHERE
    company.id = people.company AND
    workunit.id = people.unit AND
    groups.id = people.group AND
    groups.floor = 'something from textbox';

我不熟悉在多个表中组合连接语句，所以请帮助我，因为我被卡住了。

Answer 1

就这样写：

SELECT 
  people.NAME,
  people.SURNAME,
  company.NAME,
  workunit.NAME,
  groups.NAME, 
  groups.FLOOR
FROM 
  people
  INNER JOIN GROUP
    ON people.GROUP=GROUPS.id
  INNER JOIN company
    ON people.company=company.id
  INNER JOIN UNIT 
    ON people.UNIT =UNIT.id
WHERE
  GROUPS.floor='something from textbox';

Answer 2

我在SQL Server中验证了您的查询。你需要稍微修改它，以便以这种方式看它的执行：

SELECT
    people.NAME, people.SURNAME, company.NAME,
    workunit.NAME, groups.NAME, groups.FLOOR
FROM
    company, workunit, people
LEFT JOIN
    groups on people.GROUP = GROUPS.id
WHERE
    company.id = people.company AND
    workunit.id = people.unit AND
    groups.id = people.group AND
    groups.floor = 'something from textbox';

无论如何，您的查询不起作用，因为即使您希望使用LEFT JOIN描述的方式得到结果，您也要设置条件：

AND groups.floor = 'something from textbox';

通过这种方式，您将无法看到与GROUPS表不匹配的记录，因为您明确表示您希望记录中列的值floor必须等于'something from textbox'。

如果您还想要不匹配，您可以将条件替换为：

OR groups.floor = 'something from textbox';

但是你会有一些重复，而group by语句无论如何都不会起作用。然后，你必须检查你是否真的想要那些预期的结果。

我不明白为什么你也想要非匹配，即使你正在寻找使用groups.floor = 'something from textbox'的精确结果。如果你想在GUI中显示结果，我认为不匹配对用户来说是无用的信息。

Answer 3

SELECT people.NAME, people.SURNAME, company.NAME, workunit.NAME, groups.NAME, groups.FLOOR

FROM company, workunit, groups LEFT JOIN  people on people.GROUP=GROUPS.id

WHERE

company.id=people.company AND
workunit.id=people.unit AND
groups.id=people.group AND
groups.floor='something from textbox';

SQL Server：只加入一个表

3 个答案: