How to Use Index in Select Statement

How to use index in select statement?

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.

How to use index in SQL query

Firstly, do you mean you're creating the index in a stored procedure? That's a bad idea - if you run the stored procedure twice, it will fail because the index already exists.

Secondly, your query doesn't use the column mentioned in the index, so it will have no impact.

Thirdly, as JodyT writes, the query analyzer (SQL Server itself) will decide which index to use; it's almost certainly better at it than you are.

Finally, to speed up the query you mention, create an index on columns artc and atelr.

Use an index in a SELECT statement in Oracle

Contrary to the LIKE predicate that can be resolved with a index range scan there is no index access path in Oracle that would implement a NOT LIKE that would need to do two range scans before and after your LIKE value.

Let's illustrate it in this setup with a table that has only one row satisfying your not like predicate.

create table Employees as
select 'J'||rownum as First_Name, lpad('x',1000,'y') pad from dual connect by level <= 10000
union all 
select 'Xname', 'zzzzz' from dual;

create index Z7 on Employees (First_Name);

The query

SELECT * FROM Employees  WHERE First_Name NOT LIKE ('J%');

performs as expected a FULL TABLE SCAN

-------------------------------------------------------------------------------
| Id  | Operation         | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |           |    37 | 37259 |   398   (1)| 00:00:01 |
|*  1 |  TABLE ACCESS FULL| EMPLOYEES |    37 | 37259 |   398   (1)| 00:00:01 |
-------------------------------------------------------------------------------

 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   1 - filter("FIRST_NAME" NOT LIKE 'J%')

You may hint Oracle to use index as follows (note that your syntax FROM Employees WITH (INDEX(Z7)) WHERE is wrong and causing your error!)

SELECT /*+ index(Employees Z7) */ * FROM Employees  WHERE First_Name NOT LIKE ('J%');

This will indeed cause the index usage, but not in the sence you probablly intended.

If you examines the execution plan you'll see the INDEX FULL SCAN, that means, Oracle walks through the complete index from A to Z, filter the entires in the index that are not like your predicates (see the FILTER in the plan below) and for the selected keys access the table.

So generally you'll be not happy with this plan for a large index as it will take substantially longer that the full table scan.

-------------------------------------------------------------------------------------------------
| Id  | Operation                           | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                    |           |  9433 |  9276K|  2912   (1)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| EMPLOYEES |  9433 |  9276K|  2912   (1)| 00:00:01 |
|*  2 |   INDEX FULL SCAN                   | Z7        |  9433 |       |    25   (0)| 00:00:01 |
-------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
 
   2 - filter("FIRST_NAME" NOT LIKE 'J%') 

See here how to produce the execution plan for the query

How to select an sql index

This is the syntax for a table hint.

SELECT column_list FROM table_name WITH (INDEX (index_name) [, ...]);

in sql server which I think is your case based on your error.

As to whether the index will be picked up or not (both in oracle and sql server) will depend on a lot of other reasons. As the name indicates, it is just a hint to the optimizer. The cost of the query using the hint and without the hint will eventually be the deciding factors for the optimizer.

In most cases, you'll not see the need to specify the hint. The optimizer used this access path if using the index is the best way to retrieve the data and all the meta data (statistics) indicate the same.

Using index in Update Clause on Apache Ignite Sql Query

How Ignite executes these queries - at the time of writing this post - is by spliting the query into two parts:

1. SELECT with the same condition as specified in the original query.
2. Iterate over the SELECT results and update each record as specified in the SET clause.

It's usually easy to guess how the SELECT part will look like based on the original query. In your case, I'm pretty sure SELECT * FROM DB.MY_TABLE WHERE Name = 'Me' is the query that will be executed.

I would just check that EXPLAIN SELECT * FROM DB.MY_TABLE WHERE Name = 'Me' uses the index you want it to use and then trust the system to do the UPDATE correctly.

add a column from a select query with index

Since you can access the latest version of MySQL, we can simply use the Row_Number() functionality:

SELECT  
  ROW_NUMBER() OVER () AS new_column, 
  quantity 
FROM menu;

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