Page 66 - Modular_V2.0_SQL_Flipbook

Dropping an Index

To delete an existing index from a table, you can use DROP INDEX command, as shown below:

DROP INDEX index_name ON table_name;
In case you want to remove a primary key index, use the following syntax:

ALTER TABLE table_name DROP PRIMARY KEY;

Showing all existing Indexes

To view all the indexes applied on a given table, use the SHOW INDEX command as follows:

SHOW INDEX FROM table_name;
Points to remember while using indexes:

1. An SQL programmer must identify the high-volume queries that consume significant time and
resources to determine if a Full-Text Index is needed.

2. The columns chosen for indexing must be appropriately placed against the clauses (e.g., WHERE,
ORDER BY, JOIN) when creating the indexes.

3. Over-indexing does not solve any purpose, so be mindful of the number of indexes created.
4. If multiple columns need to be indexed, a composite index should be used.

Proper utilisation of SQL indexes can significantly improve the performance of your database.

Recap

A subquery can be defined as a query within another query.
A JOIN clause is used to combine rows from two or more tables based on a related column

between them.

A view is a virtual table created based on one or more tables.
An index is a structure that is used to improve the performance of database activity.

Exercise

A. Tick ( ) the correct option.
1. Which of the following can be defined as a query within another query?

a. Index b. Subquery
c. Join d. View

2. Which of the following is the correct syntax for CREATE INDEX command?
a. INSERT INDEX index_name ON table_name;

b. INSERT INDEX index_name ON database_name;

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