by Markus Winand.

Modifying Data


So far we have only discussed query performance, but SQL is not only about queries. It supports data manipulation as well. The respective commands—insert, delete, and update—form the so-called “data manipulation language” (DML)—a section of the SQL standard. The performance of these commands is for the most part negatively influenced by indexes.

An index is pure redundancy. It contains only data that is also stored in the table. During write operations, the database must keep those redundancies consistent. Specifically, it means that insert, delete and update not only affect the table but also the indexes that hold a copy of the affected data.

Contents

  1. Insert — cannot take direct benefit from indexes

  2. Delete — uses indexes for the where clause

  3. Update — does not affect all indexes of the table

Previous pageNext page

About the Author

Photo of Markus Winand

Markus Winand teaches efficient SQL—inhouse and online. He minimizes the development time using modern SQL and optimizes the runtime with smart indexing. His book entitled SQL Performance Explained has become standard reading.

Buy his Book on Amazon

Cover of “SQL Performance Explained”: Squirrel running on grass

The essence of SQL tuning in 200 pages

Buy on Amazon
(paperback only)

Paperback and PDF also available at Markus’ store.

Hire Markus

…to answer your current SQL questions.

The quick and easy way to benefit from his extensive knowledge and experience.
Learn more »

“Use The Index, Luke!” by Markus Winand is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 Unported License.
Legal | Contact | NO WARRANTY | Trademarks | Privacy | CC-BY-NC-ND 3.0 license