What is the Oracle ( ) Operator and How Does it Work in OUTER JOINs?

Understanding Oracle's ( ) Operator in Outer Joins

Oracle's ( ) operator, used in older SQL syntax for outer joins, often causes confusion. It's a non-standard operator, unlike the ANSI-standard JOIN syntax. Let's examine its function within outer join queries.

Outer Joins Explained

An outer join connects rows from two tables ('a' and 'b' in the example below) based on a join condition (e.g., a.id=b.id). Unlike an INNER JOIN, an outer join includes rows even when there's no match in the other table.

Right Outer Join with ( )

The ( ) operator in the following Oracle statement designates a right outer join:

<code class="language-sql">select ...
from a, b
where a.id = b.id(+)</code>

This query returns all rows from table 'b'. If a row in 'b' has a matching id in 'a', the corresponding row from 'a' is included. If not, the columns from 'a' will have NULL values in the result set.

Modern Alternatives

Oracle strongly advises using the ANSI-92 standard JOIN syntax, which is clearer and more robust:

ANSI-92 (Recommended):

<code class="language-sql">SELECT ...
FROM a
RIGHT JOIN b ON b.id = a.id</code>

Oracle's ( ) Syntax (Deprecated):

<code class="language-sql">select ...
from a,b
where a.id=b.id(+)</code>

Important Considerations

The ( ) operator has limitations and quirks not present in the standard JOIN syntax. For better readability, maintainability, and to avoid unexpected behavior, always prioritize the ANSI-92 JOIN syntax when writing outer join queries in Oracle.

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