How Does Oracle's ( ) Symbol in WHERE Clauses Perform Outer Joins?

Ambiguity in WHERE Clause: Understanding Oracle's Outer Join Syntax

In the context of Oracle SQL, the ( ) symbol encountered in a WHERE clause is utilized to indicate an outer join operation. It signifies a departure from the standard inner join, where matching rows from multiple tables are retrieved.

LEFT OUTER Join:
When the ( ) operator appears after the primary key table name (Table1 in this instance), it signifies a LEFT OUTER join. In such a join, all rows from the primary table are returned, regardless of whether corresponding rows exist in the secondary table (Table2). The unmatched rows in the secondary table are represented by NULL values.

RIGHT OUTER Join:
Conversely, if the ( ) operator follows the secondary table name (Table2 in the example), it denotes a RIGHT OUTER join. This results in all rows from the secondary table being retrieved, including those that lack corresponding rows in the primary table. The unmatched primary table rows, in this case, are shown as NULL.

Why Use Outer Joins?
Outer joins are employed to preserve data integrity by displaying all relevant information from both tables, even if some rows do not possess matching values. This is particularly useful when analyzing data across tables with diverse record counts.

Deprecation Note:
While the ( ) syntax was historically prevalent in Oracle, its usage is now discouraged in favor of more explicit and standards-compliant OUTER JOIN keywords. These keywords, such as LEFT OUTER JOIN or RIGHT OUTER JOIN, provide clearer readability and eliminate potential confusion in code interpretation.

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