topic Re: what is left outer join in Application Development and Automation Discussions

what is left outer join

Former Member — Sat, 21 Apr 2007 03:45:02 GMT

Hi Experts,

Tell me something about left outerjoin

Thanks in advance

Re: what is left outer join

amit_khare — Sat, 21 Apr 2007 03:49:17 GMT

Check the links -

http://help.sap.com/saphelp_erp2005/helpdata/en/cf/21ec77446011d189700000e8322d00/frameset.htm

http://help.sap.com/saphelp_nw04/helpdata/en/fc/eb39c4358411d1829f0000e829fbfe/frameset.htm

Regards,

Amit

Reward all helpful replies.

Re: what is left outer join

Former Member — Sat, 21 Apr 2007 04:10:54 GMT

A LEFT OUTER JOIN is one of the JOIN operations that allow you to specify a join clause. It preserves the unmatched rows from the first (left) table, joining them with a NULL row in the shape of the second (right) table.

Re: what is left outer join

Former Member — Sat, 21 Apr 2007 07:46:43 GMT

Hi surya

If a table C is formed from table A and table B using left outer join then table C contains both A n B values but only those rows of table A which has same value in table B in the key will b picked.

If table A doesnt find any matching value then that row is dropped n not shown in table C.

Re: what is left outer join

Former Member — Sat, 21 Apr 2007 08:25:09 GMT

Hi..

<b>Specifying Two or More Database Tables as a Left Outer Join</b>

In an inner join, a line from the left-hand database table or join is only included in the selection if there is one or more lines in the right-hand database table that meet the ON condition <cond>. The left outer join, on the other hand, reads lines from the left-hand database table or join even if there is no corresponding line in the right-hand table.

<b>SELECT...

...

FROM <tab> LEFT [OUTER] JOIN <dbtab> [AS <alias>] ON <cond>

...</b>

<tab> and <dbtab> are subject to the same rules and conditions as in an inner join. The OUTER addition is optional. The tables are linked in the same way as the inner join with the one exception that all lines selected from <tab> are included in the final selection. If <dbtab> does not contain any lines that meet the condition <cond>, the system includes a single line in the selection whose columns from <dbtab> are filled with null values.

In the left outer join, more restrictions apply to the condition <cond> than in the inner join. In addition to the above restrictions:

EQ or = is the only permitted relational operator.

There must be at least one comparison between columns from <tab> and <dbtab>.

The WHERE clause may not contain any comparisons with columns from <dbtab>. All comparisons using columns from <dbtab> must appear in the condition <cond>.

Client Handling

Re: what is left outer join

Former Member — Sat, 21 Apr 2007 09:21:32 GMT

Hi ,

check out it may help you

check this link

http://dev.mysql.com/doc/maxdb/en/bf/692940cbf2195de10000000a1550b0/frameset.htm

reward helpful answers ,

regards,

Venkat

Message was edited by:

venkata chalapathi

Re: what is left outer join

Former Member — Sat, 21 Apr 2007 09:30:15 GMT

left outer join will give all the possible combinations between tables even if the fields are empty inthe tables.

regards,

padma

Re: what is left outer join

Clemenss — Sat, 21 Apr 2007 12:15:41 GMT

Surya,

please no not enter "left outer join" in the "Search Forum" field above. This could lead you to lots of information about your topic and would keep you from annoying people.

Regards,

Clemens

Re: what is left outer join

Former Member — Sat, 21 Apr 2007 21:39:52 GMT

Hi Surya..!!

if you are still not satisfied with the above answers...please find below a different explanation..

think there are two tables A and B.. and let us represent these 2 sets as two circles with an intersection area ( remember the mathematic diagram of A Union B and A intersection B )

now A is the left circle

B is the right circle.

Left Outer Join is :

The area covered by A ( including A^ B)

Right Outer Join is :

The area covered by B ( including A^ B)

Inner Join is :

only A ^ B

Cheers

Kesari