Sqlitestudio book9/10/2023 ![]() ![]() Columns that are frequently manipulated.SQLite Studio is an open source, compact, standard and easy to install cross-platform database management system.Columns that contain a high number of NULL values.Tables that have frequent, large batch update or insert operations.The following guidelines indicate when the use of an index should be reconsidered. You can use the following statement to delete previously created index.Īlthough indexes are intended to enhance the performance of a database, there are times when they should be avoided. Care should be taken when dropping an index because performance may be slowed or improved.įollowing is the basic syntax is as follows − Sqlite> SELECT * FROM sqlite_master WHERE type = 'index' Īn index can be dropped using SQLite DROP command. You can list down all the indexes database wide as follows − This will produce the following result, where sqlite_autoindex_COMPANY_1 is an implicit index which got created when the table itself was created. Now, let's list down all the indices available in COMPANY table using. ![]() ![]() Sqlite> CREATE INDEX salary_index ON COMPANY (salary) Indexes are automatically created for primary key constraints and unique constraints.įollowing is an example where we will create an index in COMPANY table for salary column − Implicit indexes are indexes that are automatically created by the database server when an object is created. ![]() Should there be two or more columns that are frequently used in the WHERE clause as filters, the composite index would be the best choice. Should there be only one column used, a single-column index should be the choice. Whether to create a single-column index or a composite index, take into consideration the column(s) that you may use very frequently in a query's WHERE clause as filter conditions. The basic syntax is as follows −Ī composite index is an index on two or more columns of a table. A unique index does not allow any duplicate values to be inserted into the table. Unique indexes are used not only for performance, but also for data integrity. The CREATE INDEX Commandįollowing is the basic syntax of CREATE INDEX.Ī single-column index is one that is created based on only one table column. Indexes can also be unique, similar to the UNIQUE constraint, in that the index prevents duplicate entries in the column or combination of columns on which there's an index. Indexes can be created or dropped with no effect on the data.Ĭreating an index involves the CREATE INDEX statement, which allows you to name the index, to specify the table and which column or columns to index, and to indicate whether the index is in an ascending or descending order. An index in a database is very similar to an index in the back of a book.įor example, if you want to reference all pages in a book that discuss a certain topic, you first refer to the index, which lists all topics alphabetically and are then referred to one or more specific page numbers.Īn index helps speed up SELECT queries and WHERE clauses, but it slows down data input, with UPDATE and INSERT statements. Simply put, an index is a pointer to data in a table. Indexes are special lookup tables that the database search engine can use to speed up data retrieval. ![]()
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