Re: equijoin select statement

On Sat, 25 Dec 2004 17:11:30 +0100, vertigo wrote:

> Hello
>
> 1. What is difference between euijoin and none quijoin select statement ?

This, together with lots of examples, is in the SQL Reference manual at http://tahiti.oracle.com ... you really should rtfm for details, as this is a very, very important concept. A quick overview, with many gaps:

Define 'Join', then define 'Equi' (equals)

A convenient definition for join is the ability to relate (match up) two or more tables, views or other data sets to provide a new data set.

Without restrictions, a join will yield a set which matches up each entry (row) from one set to all other entries in all other referenced sets. (This is called a cross-product)

Equijoin is the restriction that some of the data (one or more columns) must match in each source set. It is traditionally invoked by a where clause similar to "columnA1=columnA2 [and columnB1=columnB2 ...]"

A non-equijoin changes the restriction by requiring a specific mismatch, for example "columnA1<columnB1"

ANSI SQL moves the join from the where-clause to it's own area in the SQL statement.

>
> 2. I often find term: 'y operator'. What is it ?
>

It's frequently a place-holder to help keep the amount of documentation to a minimum. Replace 'y operator' with the one that makes the request work. Received on Sat Dec 25 2004 - 10:58:11 CST