Union two tables only if one table has data 2

[1tufgt]

What would be the best process to union two tables together based on if Table A has data I would only pull data from Table B?

SELECT Column A, Column B, Column C FROM Table A
union
Select Column A, Column B, Column C FROM Table B

So in the end I need to union two tables but only pull data if data is returned from Table A.

 

[bborissov]

SELECT * FROM TableA
UNION ALL
SELECT * FROM TableB
WHERE (SELECT COUNT(*) FROM TableA) > 0

Borislav Borissov
VFP9 SP2, SQL Server

 

[1tufgt]

bborissov, to take it another step further how would I only pull from Table B only if Column A is found in Table A.

 

[bborissov]

Select Column A, Column B, Column C FROM Table B
WHERE EXISTS(SELECT * FROM INFORMATION_SCHEMA.Columns WHERE Table_Name = 'TableA' AND Column_Name = 'ColumnA')

Borislav Borissov
VFP9 SP2, SQL Server

 

[Andrzejek]

You may also look at these Visual Representation of SQL Joins

This article describes SQL Joins in a visual manner, and also the most efficient way to write the visualized Joins.

---- Andy

There is a great need for a sarcasm font.

 

[1tufgt]

bborissov, thanks that's what I was looking for.

Andrzejek, thanks for the info on the joins. I already have a printout of those joins and was struggling with only selecting after a initial select.