Writing or Choosing Strategy and Support Functions

In a query, the WHERE clause might specify a strategy function to qualify or filter rows. The following clauses represent the same strategy function, which compares the index key cost to a constant:

WHERE equal(cost, 100)
WHERE cost = 100

Support functions build and scan the index and can perform any of the following tasks for a secondary access method:

• Build an index
• Search for specific key values
• Add and delete index entries
• Reorganize the index to accommodate new entries

The access method can call the same support function to perform multiple tasks. For example, an access method might call a between() support function to retrieve keys for the WHERE clause to test and locate the entries immediately greater than and less than a new index entry for an INSERT command.