从第一个表中选择任何内容

Question

Quick question regarding sql syntax If I have 3 tables (hereby reffered to 1,2,3) and want to select everything from table 2,3 tables depending on if an id is present in table 1, how do I do that, IE "select nothing" from table 1? As for now I select everything from table 1 .

SELECT * FROM [Content] pc, [test] Dc, 
[Swg] Swg where pc.Id=Dc.Id and pc.Id=Swg.Id  order by pc.Id

Answer 1

If I understand you correctly, you want to select everything from tables test and SWG, even if there is no match in table Content?

If so, a RIGHT join would do the trick:

SELECT
  *
FROM
   Content
      RIGHT JOIN test ON content.ID = test.ID
      RIGHT JOIN SWG ON Content.ID = SWG.ID

If you're looking for everything from test and SWG but only if there is a matching ID in CONTENT, then this should work:

SELECT 
    test.*
    , SWG.*
FROM
   Content
      JOIN test ON content.ID = test.ID
      JOIN SWG ON Content.ID = SWG.ID

Answer 2

So you just don't want to see the columns from table 1?

SELECT Dc.*, Swg.*
FROM [Content] pc, [test] Dc, 
[Swg] Swg where pc.Id=Dc.Id and pc.Id=Swg.Id  order by pc.Id

That assumed pc = table 1, dc = table 2 and swg = table 3

Answer 3

eg if table 1 is Content (pc alias in your query):

SELECT Dc.*, swg.*
FROM ....

So, you have to specify the table aliases you want to select from. * alone will select all columns from all referenced tables

Answer 4

You may Tried This

SELECT pc.* ,Dc.* ,Swg.* FROM [Content] pc, [test] Dc, [Swg] Swg where (pc.Id=Dc.Id or pc.Id=Swg.Id) order by pc.Id

Answer 5

Select * from 
T1 left join T2 on T1.id=T2.id 
Where T1.id in (select id from T3 where...etc.)

This way, you will get everything from T1 , and matching T2 values if T1 values matches values from T3 without getting this T3 table values