Why does the same query takes different amount of time to run?

Either you are getting different performance because the system is under a different sort of load, you are getting different performance because of data volume changes, or you are getting different performance because you are getting different query plans.

How do I make my query run faster?

Here are some key ways to improve SQL query speed and performance.

1. Use column names instead of SELECT *
2. Avoid Nested Queries & Views.
3. Use IN predicate while querying Indexed columns.
4. Do pre-staging.
5. Use temp tables.
6. Use CASE instead of UPDATE.
7. Avoid using GUID.
8. Avoid using OR in JOINS.

Are parameterized queries faster?

In this example, parameterized queries are shown to run about 33\% faster than the dynamic SQL option. A more important and wider performance gap is seen on the amount of CPU time used. The dynamic SQL uses roughly 3.3 times the amount of CPU on the database server as the parameterized query option.

Why might an SQL query suddenly begin to perform much slower than usual standards?

It is important to make sure that there are no maintenance tasks are running when queries are suddenly getting slower. I have often seen when backup jobs, statistics update or index maintenance tasks start they create resource crunch of IO, which leads to temporarily slow down of queries.

How do you optimize a slow running query?

It’s vital you optimize your queries for minimum impact on database performance.

1. Define business requirements first.
2. SELECT fields instead of using SELECT *
3. Avoid SELECT DISTINCT.
4. Create joins with INNER JOIN (not WHERE)
5. Use WHERE instead of HAVING to define filters.
6. Use wildcards at the end of a phrase only.

What is a slow query?

The slow query log consists of SQL statements that take more than long_query_time seconds to execute and require at least min_examined_row_limit rows to be examined. The slow query log can be used to find queries that take a long time to execute and are therefore candidates for optimization.

How do you optimize a slow query?

Why is MY SQL query taking so much time to run?

When you are not hardcoding it and run it through the procedure and if you are trying to derive the value from the input value then it might take more time. 2) In rare cases it can be due to network traffic, also where we will not have consistency in the query execution time for the same input data.

How to make a query faster than the SP?

If you run the query itself when there’s a light load, it will be better than when you run the SP during a heavy load. Also, to ensure the query truly is quicker than the SP, you need to rule out data/execution plan caching which makes a query faster for subsequent runs. You can clear the cache out using: DBCC FREEPROCCACHE DBCC DROPCLEANBUFFERS

What is the basic execution flow of a SQL query?

The basic execution flow is that it SELECTS INTOsome data into temp tables declared with he #sign and then runs a cursor through these tables a generate a ‘running total’ into a third temp table which is created using CREATE. Then this resulting temp table is joined with other tables in the DB to generated the result after some grouping etc.