Select 2 tables

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Select 2 tables

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SQLSACT

Posted Monday, September 17, 2012 12:22 AM

Ten Centuries

Group: General Forum Members
Last Login: Today @ 7:48 AM
Points: 1,200, Visits: 2,126

Hi All

Consider the following 2 tables

create table T1
(Col1 int, Col2 int)
go
create table T2
(Col3 int, Col4 int)

And the following query

select Col1, Col4 from T1,T2

What is actually happening when the select statement is executed? Is it an inner join or left join?

Thanks

Post #1359987

Jason-299789

Posted Monday, September 17, 2012 12:43 AM

SSC Eights!

Group: General Forum Members
Last Login: Yesterday @ 1:30 AM
Points: 803, Visits: 2,124

You are doing a Cross join so what will happen is that you will get T1 rowcount * t2 Count

Eg if you had 2 rows in T1 and 4 in T2 you would get 8 rows returned with data something like this returned

T1 T2
1 1
1 2
1 3
1 4
2 1
2 2
2 3
2 4

To turn it into an Inner join you need to do

Select Col1, Col4
From T1,T2
Where
T1.Col1=T2.Col3

Or a Left Join then this

Select Col1, Col4
From T1,T2
Where
T1.Col1*=T2.Col3

for a right outer the clause is =*, Unfortunately I cant remember the syntax for a Full outer.

I believe this style of left/right outer join syntax (*= etc) is being depricated over the next couple of releases of SQL server, in 2008 there is a server setting to allow the syntax, im not sure about SQL 2012 though

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Post #1359990

rhythmk

Posted Monday, September 17, 2012 12:49 AM

Old Hand

Group: General Forum Members
Last Login: Saturday, November 10, 2012 9:30 AM
Points: 388, Visits: 603

SQLSACT (9/17/2012)

Hi All

Consider the following 2 tables

create table T1
(Col1 int, Col2 int)
go
create table T2
(Col3 int, Col4 int)

And the following query

select Col1, Col4 from T1,T2

What is actually happening when the select statement is executed? Is it an inner join or left join?

Thanks

Neither inner nor left join. It would be a cross join.

--rhythmk
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Post #1359992

SQLSACT

Posted Monday, September 17, 2012 1:01 AM

Ten Centuries

Group: General Forum Members
Last Login: Today @ 7:48 AM
Points: 1,200, Visits: 2,126

Thanks

Post #1359999

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