Contents
Should we index status column?
If you have other fields in the where clause, a composite index should work better. Having the status field there depends also on the fact if it is being updated (often) since that will then require maintaining the index too. One option is to add the fields you have in select part as included columns.
How many columns can be indexed on a table?
Currently, you can have no more than 16 key columns in an index, and altogether those key columns cannot exceed the maximum index size of 900 bytes. Included columns can be data types that are not allowed as index columns.
What to do when column does not have index?
Use the NOT NULL attribute for those columns in which you consider the indexing, so that NULL values will never be stored. Use the –log-long-format option to log queries that aren’t using indexes. In this way, you can examine this log file and adjust your queries accordingly.
Is there a danger in indexing too many columns?
The only real danger in indexing too many columns is slowing down changes to rows in large tables, as the indexes all need updating too. If you’re really not sure what to index, just time your slowest queries, look at what columns are being used most often, and index them.
When to use row Num or column NUM in index?
If array contains only one row or column, the corresponding row_num or column_num argument is optional. If array has more than one row and more than one column, and only row_num or column_num is used, INDEX returns an array of the entire row or column in array. row_num Required, unless column_num is present.
Do you have to index all columns in MySQL?
Only index those columns that are required in WHERE and ORDER BY clauses. Indexing columns in abundance will result in some disadvantages. Try to take benefit of “index prefix” or “multi-columns index” feature of MySQL. If you create an index such as INDEX (first_name, last_name), don’t create INDEX (first_name).