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How to use index in select statement?

sql
indexing
database-performance
query-optimization
Anton ShumikhinbyAnton Shumikhin·Jan 2, 2025
TLDR

In your SELECT query, align the WHERE clause conditions to match the indexed column(s). For instance, if an index exists on users(email), structure your query as:

SELECT * FROM users WHERE email = '[email protected]'; -- Enjoying your email inbox, yet? 😄

This direct matching method enables the database to efficaciously use the index, bypassing a full table scan. Watch out though, any functions applied on email may negate the index's efficiency.

Have a hint of index

Sometimes the DB engine's auto-index picking doesn't satisfy your cutting-edge taste. Have no fear, you can give it a hint!

Crafting the hint

Simply include the index name along with the WITH(INDEX(your_index)) clause in your SELECT query.

SELECT * FROM users WITH(INDEX(IX_Email)) -- Who needs GPS when you've got an index, right? WHERE email = '[email protected]';

Hints are no mandates!

Remember, index hints are like spices in a recipe—you don't want to use them excessively. They bind your query to a particular index, compromising your database's flexibility over time.

Obviously, hints have benefits

The WITH(INDEX()) hint can be as handy as a swiss knife when checking whether a fresh index improves performance or for enforcing the use of an index knowing its specifics.

Indexing pitfalls and fine tunings

  • Unique Index: If your column has more unique values than the galaxies in the universe, index it.
  • Selective Indexing: Index those columns involved in the most dramatic SQL JOINs and WHERE scenes.
  • Weighing the Costs: If the width of your table reminds you of an interstellar travel delay, opt for different strategies.
  • Always Monitor: Keep a keen eye on query performance. Remember, forcing isn't always the solution. Sometimes, it's patience and balance.

Query patterns and their index soulmates

Understanding the stride of your queries is the first step to index nirvana. Some patterns like range conditions or sorting requirements may beckon specific types of indexes like composite or included columns indexes.

Courting the right index

- Equality conditions, they're like vows (`WHERE status = 'Active'`) - Range conditions, they're like planning a future together (`WHERE created_at BETWEEN '2021-01-01' AND '2021-12-31'`) - Order by columns, picking the perfect setting for that special dinner (☺️)

Queries with an indexing phobia

- Non-indexed columns - Columns masquerading in functions - Wildcard `LIKE` searches not starting consistently

Advanced index maneuvers: hints and forcing

For complex systems or troubling query plans, calling in the cavalry in the form of index hints or forcing can be the silver bullet.

Forcing an index

Force an index like your favorite superhero: - SQL Server: `WITH(INDEX(idx_name))` - MySQL: `FORCE INDEX (idx_name)`

Advanced indexing survival kit

  • Test your queries: They're your control group and guinea pigs.
  • Documentation: It's your friendly neighborhood manual.
  • Overforcing is overkill: Trust the optimizer as your faithful ally.