For questions pertaining to the measurement or improvement of a SQL query (that deals with speed).
If you're asking "Why is my SQL query so slow?" or something like that, you need to do a little extra homework to get good answers from the Stack Overflow community.
What database?
Put this query-performance tag on your question along with the tag for your database: sql-server, mysql. postgresql, oracle or whatever database you use. Don't use more than one database tag, please. Optimization works somewhat differently from database to database.
How many rows and how fast?
Please figure out approximately how many rows you expect in your result set, and approximately how many rows are in each table involved with the query. Mention those numbers in your question. Please mention how long you hope your query needs to take, and how long it's taking. (That is, tell us what you mean by slow).
Don't oversimplify
Don't try to simplify your question by replacing your actual SELECT column lists with *. Using * in SELECT clauses can be harmful to query performance compared to specifying the list of columns you need.
Show your table definitions, with indexes
In your question include your table definitions and index definitions for each table and view involved in your query. Make sure your question shows all indexes in all relevant tables. When you're asking a performance question, please don't oversimplify your question by omitting indexes or columns you think might be irrelevant. The strangest things can be relevant to performance!
Show your database's explanation of how it satisfied your query
In your question please show the EXPLAIN PLAN output (it's just EXPLAIN in some table server makes and models) for your query.
Reference
Please be aware that query performance optimization can be an inexact science. This is a good reference. http://use-the-index-luke.com/
