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writing t-sql joins

Posted on 2014-03-25
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Last Modified: 2014-03-25
I can re-write an inner join statement as below:
inner join statement:
  SELECT t1.id, t2.id
  FROM table1 t1
  JOIN table2 t2 on t1.id = t2.id

same statement:
  SELECT t1.id, t2.id
FROM table1, table2
WHERE table1.id = table2.id AND

Are there other joins I rewrite and is there any advantage to doing so?
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Question by:dhenderson12
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PortletPaul earned 500 total points
ID: 39953171
You should use the top (first) example which is "ANSI join syntax".

The lower example is also allowed and pre-dates adoption of the ANSI standard - but it is a flawed approach and isn't considered best practice today.
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Author Comment

by:dhenderson12
ID: 39953192
why is it a flawed approach?
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Expert Comment

by:PortletPaul
ID: 39953194
why is it flawed? try this:

oops, forgot something - but it still runs as a query (as a Cartesian join)
  SELECT t1.id, t2.id
FROM table1, table2

the equivalent is:
  SELECT t1.id, t2.id
  FROM table1 t1
  JOIN table2 t2 on

it doesn't let you forget the needed conditions.
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Author Comment

by:dhenderson12
ID: 39953203
I see the problem. Thanks.
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LVL 48

Expert Comment

by:PortletPaul
ID: 39953206
& Let me put it another way.

I would not hire anyone who does not use and understand ANSI join syntax. No exceptions.
I (and the company I work for) will not permit non-ANSI syntax in any of our products.

ANSI join syntax is far better for documenting the query logic and for maintaining the SQL.
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