How do I optimize a select COUNT query?

How do I optimize a select COUNT query?

Optimize MySQL COUNT (*) query

1. SELECT COUNT(*) from table1 WHERE field1 IN (‘val1′,’val2’) OR field2 IN (‘val3′,’val4’);
2. ALTER TABLE table1 ADD INDEX `field1_field2_idx` (`field1`,`field2`);
3. ALTER TABLE table1 ADD INDEX `field2_idx` (`field2`);

Is COUNT distinct bad?

In MySQL < 5.5, SELECT COUNT(DISTINCT(xyz)) has really bad performance. SELECT COUNT(*) FROM (SELECT DISTINCT base_dir FROM {boost_cache} GROUP BY base_dir) AS counted; Note that an alias (“AS counted”) is required. This query takes 1-2 seconds on the same test database.

Does select count lock table?

select count(*) will create a shared lock on the whole table but it should release as soon as the operation is complete.

Which is faster having or where?

You can use HAVING but recommended you should use with GROUP BY . SQL Standard says that WHERE restricts the result set before returning rows and HAVING restricts the result set after bringing all the rows. So WHERE is faster.

How to optimize count ( * ) in SQL Server?

[VProcessStatus] WITH SCHEMABINDING AS select processstatus, StatusCount = COUNT_BIG (*) FROM DBO.tbltaxtransaction GROUP BY processstatus GO GRANT SELECT ON [dbo]. [VProcessStatus] TO [mydomain\\itdevelopment] AS [dbo] GO CREATE UNIQUE CLUSTERED INDEX [IDX_VProcessStatus] ON [dbo].

Which is faster count ( * ) or count ( 1 )?

Clearly, COUNT (*) and COUNT (1) will always return the same result. Therefore, if one were slower than the other it would effectively be due to an optimiser bug. Since both forms are used very frequently in queries, it would make no sense for a DBMS to allow such a bug to remain unfixed.

How to select count ( * ) from something Records?

SELECT COUNT (*) FROM something counts records which is an easy task. SELECT COUNT (1) FROM something retrieves a 1 per record and than counts the 1s that are not null, which is essentially counting records, only more complicated.

What’s the difference between Count ( 1 ) and Count ( * )?

There is an article showing that the COUNT (1) on Oracle is just an alias to COUNT (*), with a proof about that. There is a part of the database software that is called “The Optimizer”, which is defined in the official documentation as “Built-in database software that determines the most efficient way to execute a SQL statement“.