sql statement select what cant be joined

Posted on 2014-07-18
Last Modified: 2014-07-20

I have 2 tables:

**** TableA ****

NameA    valueA
-------  --------
john     10
mary     20
jack     30
tom       5

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*** TableB ****

NameB    valueB
-------  --------
Sarah    10
Thomas   30
Ive      9

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I know how to join this tables and get the ones that have the same value, I do it this way and get the following data:

select * from tableA inner join tableB on tableA.valueA = tableB.valueB

John 10 Sarah 10
Jack 30 Thomas 30

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Q1. How do I get only the ones present in table A, in this example:
Tom 5
    Mary 20

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Q2. How do I get only the ones present in table B, in this example:

Ive 9

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Question by:jsbx
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LVL 22

Assisted Solution

by:Steve Wales
Steve Wales earned 100 total points
ID: 40205225
There are several ways to get this data, have a read of this article: How to find rows that are in one table, but not another which shows you several ways to do it.

You can use NOT IN, NOT EXISTS, a LEFT JOIN checking for NULL values or the EXCEPT operator (for SQL Server)

Expert Comment

by:Philip Portnoy
ID: 40205239
Do you have a unique value in the tables? If you do then it's very easy.
Let's assume your name is a unique value.

For these values from tableA:
select * from tableA where name NOT IN (select from tableA inner join tableB on tableA.valueA = tableB.valueB) AND name NOT IN (select from tableA inner join tableB on tableA.valueA = tableB.valueB)

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For values from tableB:
select * from tableB where name NOT IN (select from tableA inner join tableB on tableA.valueA = tableB.valueB) AND name NOT IN (select from tableA inner join tableB on tableA.valueA = tableB.valueB)

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Please note that the fact that I don't know your database structure and what's the data in there this code is really "dirty" and might require optimization.

Author Comment

ID: 40205259
testing ...
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LVL 32

Expert Comment

ID: 40205439
As pointed out there are severla ways to do this. Here is one -
For Q1
select * from tableA
where valueA in
(select valueA from tableA except select valueA from tableB)

For Q2
select * from tableb
where valueb in
(select valueB from tableB except select valueA from tableA)
LVL 69

Accepted Solution

Scott Pletcher earned 400 total points
ID: 40205441
This query will show you the full combination -- both, or either one -- and which table, or both, had data:

    COALESCE(a.nameA, b.nameb) AS Name,
    COALESCE(a.valueA, b.valueB) AS Value,
        WHEN a.nameA IS NULL THEN 'Only in B'  --or 'Missing from A'
        WHEN a.nameB IS NULL THEN 'Only in A'  --or 'Missing from B'
        ELSE 'In both A and B' END  --or 'Not missing in either'
        AS In_Which_Table
FROM tableA a
    b.nameB = a.nameA
LVL 32

Expert Comment

ID: 40205448
And another way -
select * from TableA as a
where not exists
(select 1 from tableB as b
 where a.valueA = b.valueB)

select * from TableB as b
where not exists
(select 1 from tableA as a
 where a.valueA = b.valueB)

Author Closing Comment

ID: 40205487
Thanks to all.
LVL 48

Expert Comment

ID: 40206882
Was this homework? I'm surprised no-one asked.

I'm also surprised no-one offered this: the visual chart available here is very useful

Author Comment

ID: 40207355
No it wasn't.
I just simplified the question in order to avoid misunderstandings since english is not my native lang.

Author Comment

ID: 40207367
Portlet paul
Anyway the article you pointed is remarkable.  Thanks.

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