DB2 Query Writing Best Practices

Problem

Writing efficient SQL SELECTqueries for DB2 can be tricky. Some general SQL guidelines apply, and there are also specific practices that apply only to DB2.

Solution

Here is a list of tips you can use to write good SELECT queries:

• Avoid SELECT * in your queries. Instead, state the columns you want to select.
• Use the consistent acronyms to alias your table names (makes it easier to read joins)
• Use FETCH ONLY x ROWS to limit the results set
• Use CASE or MERGE instead of UNION ALL

References

• Efficient SELECT statements
• Writing and Tuning Queries for Optimal Performance