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Introduction to SQL - Part 9- SQL Index

 SQL Index

  • Indexes are special lookup tables. It is used to retrieve data  from the database very fast.
  • An Index is used to speed up select queries and where clauses. But it shows down the data input with insert and update statements. Indexes can be created or dropped without affecting the data.
  • An index in a database is just like an index in the back of a book.

Create Index statement

        CREATE INDEX index_name ON table_name (column1, column2, ...);

Unique Index statement

Syntax

        CREATE UNIQUE INDEX index_name ON table_name (column1, column2, ...);

Example

        CREATE UNIQUE INDEX websites_idx ON websites (site_name);

Drop Index Statement

Syntax

        DROP INDEX index_name;

Example    

        DROP INDEX websites_idx;

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