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I've been using indexes on my MySQL databases for a while now but never properly learnt about them. Generally I put an index on any fields that I will be searching or selecting using a WHERE clause but sometimes it doesn't seem so black and white. What are the best practices for MySQL indexes? Example situations/dilemmas:
To find the rows matching a WHERE clause quickly.. To eliminate rows from consideration. If there is a choice between multiple indexes, MySQL normally uses the index that finds the smallest number of rows (the most selective index). If the table has a multiple-column index, any leftmost prefix of the index can be used by the optimizer to look up rows.
4 sty 2023 · You can support more complex queries through indexes by understanding how MySQL chooses which indexes to use and when to use them. To learn more about that, refer to the MySQL documentation on indexes .
Here’s the basic syntax for using the USE INDEX hint: SELECT select_list FROM table_name USE INDEX (index_list) WHERE condition; Code language: SQL (Structured Query Language) (sql) In this syntax, the USE INDEX instructs the query optimizer to use one of the named indexes to find rows in the table.
The following queries use the index to resolve the ORDER BY part: SELECT * FROM t1 WHERE key_part1=constant ORDER BY key_part2; If you had a single column index (accountid), a filesort would be used instead. Therefore, your query does benefit from that index.
MySQL allows you to create a composite index that consists of up to 16 columns. A composite index is also known as a multiple-column index. The query optimizer uses the composite indexes for queries that test all columns in the index, or queries that test the first columns, the first two columns, and so on.
Creating and Managing MySQL indexes. This section explains what an index is and shows you how to create, modify, and drop an index. Creating indexes – introduce the index concept and show you how to create an index for one or more columns of a table.
