Chapter 15 DBMS-Specific Features
IQ join indexes are a special type of index used in Sybase AS IQ. A join index represents a full outer join of two or more tables. The query engine may use this full outer join as a starting point for queries that include left outer, right outer, and inner joins.
A full outer join is one where all rows from both the left and right specified tables are included in the result, with NULL returned for any column with no matching value in the corresponding column.
Join indexes are defined from references. You can create a join index for any set of columns that your users commonly join to resolve queries.
While some references are based on keys, Sybase AS IQ allows you to create user-defined references to include the exact join required by your foreseen queries.
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