Contents
Can MySQL use multiple indexes in one query?
MySQL can use multiple-column indexes for queries that test all the columns in the index, or queries that test just the first column, the first two columns, the first three columns, and so on. The name index is an index over the last_name and first_name columns.
What are duplicate indexes in SQL Server?
Duplicate indexes are indexes of same type, created on the same set of key columns in the same order, and same set of non-key columns (also known as included columns) with same or different order, but have different names. We should not create duplicate indexes on the table, and remove them if you find them.
Is it possible to use multiple indexes in MySQL?
Yes, MySQL can use multiple index for a single query. The optimizer will determine which indexes will benefit the query. You can use EXPLAIN to obtain information about how MySQL executes a statement. You can add or ignore indexes using hints like so:
Can a query have more than one index?
Classically, MySQL can use one index per table reference in a given query. However, in more recent versions of MySQL, an operation called an index merge can take place and allow MySQL to use more than one index per table. http://openquery.com/blog/mysql-50-index-merge-using-multiple-indexes.
What does it mean to have multiple indexes in one column?
Having multiple indexes, each on a single column may mean that only one index gets used at all – you will have to refer to the execution plan to see what effects different indexing schemes offer. You can also use the tuning wizard to help determine what indexes would make a given query or workload perform the best.
Can a zip index be used in SQL Server?
If you search by zip alone quite a lot then the above index will not be used (by SQL Server anyway) as zip is the third part of that index and the query optimiser will not see that index as helpful. You could then create an index on Zip alone that would be used in this instance.