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Lets say in the employee table, I have created an index(idx_name) on the emp_name column of the table.
Do I need to explicitly specify the index name in select clause or it will automatically used to speed up queries.
If it is required to be specified in the select clause, What is the syntax for using index in select query ?
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SQL Server CREATE INDEX statement In this syntax: First, specify the name of the index after the CREATE NONCLUSTERED INDEX clause. Note that the NONCLUSTERED keyword is optional. Second, specify the table name on which you want to create the index and a list of columns of that table as the index key columns.
It is recommended to start indexing the table by creating a clustered index, that covers the column(s) called very frequently, which will convert it from the heap table to a sorted clustered table, then create the required non-clustered indexes that cover the remaining queries in the system.
Indexing makes columns faster to query by creating pointers to where data is stored within a database. Imagine you want to find a piece of information that is within a large database. To get this information out of the database the computer will look through every row until it finds it.
They're only identical if the selected column is the PK, since COUNT(*) will use the PK index.
If you want to test the index to see if it works, here is the syntax:
SELECT * FROM Table WITH(INDEX(Index_Name)) The WITH statement will force the index to be used.
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Good question,
Usually the DB engine should automatically select the index to use based on query execution plans it builds. However, there are some pretty rare cases when you want to force the DB to use a specific index.
To be able to answer your specific question you have to specify the DB you are using.
For MySQL, you want to read the Index Hint Syntax documentation on how to do this
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