Query Optimization Options
By default, the InterSystems SQL query optimizer uses sophisticated and flexible algorithms to optimize the performance of complex queries involving join operations and/or multiple indexes. In most cases, these defaults provide optimal performance. However, after consultation with the InterSystems Worldwide Resource Center (WRC), you may be instructed to give “hints” to the query optimizer, specifying one or more aspects of query optimization. The optimize-hint argument in the FROM is used to specify these hints. You can specify multiple optimization hints in any order, separated by blank spaces. For further details, refer to Specify Optimization Hints in Queries.
You can use optimize-hint FROM clause keywords in a simple SELECT statement, in a CREATE VIEW view definition SELECT statement, or in a subquery SELECT statement within the FROM clause.
