Select 2 tables

• SQLSACT

  SSC-Insane

  Points: 21838

  More actions

  September 17, 2012 at 12:22 am

  #281887

  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

• Jason-299789

  SSC-Insane

  Points: 21601

  More actions

  September 17, 2012 at 12:43 am

  #1538411

  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

  _________________________________________________________________________
  SSC Guide to Posting and Best Practices

• rhythmk

  SSCertifiable

  Points: 7271

  More actions

  September 17, 2012 at 12:49 am

  #1538412

  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
  ------------------------------------------------------------------
  To post your question use below link
  
  https://www.sqlservercentral.com/articles/forum-etiquette-how-to-post-datacode-on-a-forum-to-get-the-best-help
  🙂

• SQLSACT

  SSC-Insane

  Points: 21838

  More actions

  September 17, 2012 at 1:01 am

  #1538417

  Thanks