Create indexes on one or more columns in a table to help SQL server find the data quickly in a query.
An index helps speed up SELECT queries and WHERE clauses, but it slows down data input, with UPDATE and INSERT statements.
CREATE INDEX index_name ON table_name (column_name);
CREATE INDEX index_name
on table_name (column1, column2);
You should only add those indexes for which you‘re sure that they‘re necessary. To determine the columns where you could put indexes on, you could:
- add indexes to columns that are foreign keys
- add indexes to columns that are often used in where clauses
- add indexes to columns that are used in order by clauses.
SQL aggregate functions:
AVG(), MIN(), MAX(), COUNT()...