Exclusion Join -- SQL Operators That Often Cause an Exclusion Join Operation
Exclusion join is a product, merge, or hash join where only the rows that do not satisfy (are NOT IN) any condition specified in the request are joined.
In other words, exclusion join finds rows in the first table that do not have a matching row in the second table.
Exclusion join is an implicit form of the outer join.
Exclusion product joins with dynamic row partition elimination are not supported for8-byte partitioning.
Also see Inclusion and Exclusion Product Joins With Dynamic Row Partition Elimination.
The following SQL specifications frequently cause the Optimizer to select an exclusion join:
- Use of the NOT IN logical operator in a subquery.
- Use of the EXCEPT and MINUS set operators.
Exclusion Joins and NULLABLE Columns
To avoid returning join rows that are null on the join column, use one of the following methods:
- When you create a table, define any columns that might be used for NOT IN join conditions as NOT NULL.
- When you write a query, qualify a potentially problematic join with an IS NOT NULL specification. For example:
WHERE Customer.CustAddress IS NOT NULL
Types of Exclusion Join
- Exclusion merge join (see Exclusion Merge Join)
- Exclusion product join (see Exclusion Product Join)
- Exclusion hash join (see Hash Join)