Fastest way to determine if record exists

Question

As the title suggests    I m trying to figure out the fastest way with the least overhead to determine if a record exists in a table or not    Sample query   SELECT COUNT    FROM products WHERE products id           vs  SELECT COUNT products id  FROM products WHERE products id           vs  SELECT products id FROM products WHERE products id        Say the   is swapped with  TB100     both the first and second queries will return the exact same result  say    1 for this conversation   The last query will return  TB100  as expected  or nothing if the id is not present in the table    The purpose is to figure out if the id is in the table or not  If not  the program will next insert the record  if it is  the program will skip it or perform an UPDATE query based on other program logic outside the scope of this question   Which is faster and has less overhead   This will be repeated tens of thousands of times per program run  and will be run many times a day      Running this query against M  SQL Server from Java via the M  provided JDBC driver

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SELECT COUNT    FROM products WHERE products id        This is the cross relational database solution that works in all databases

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create or replace procedure ex j in number  as i number  begin select id into i from student where id j  if i is not null then dbms output put line  exists    end if  exception    when no data found then         dbms output put line i    does not exists     end

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For MySql you can use LIMIT like below  Example shows in PHP     sql    quot SELECT column name FROM table name WHERE column name    your value  LIMIT 1 quot      result    conn- gt query  sql     if   result - gt  num rows  gt  0          echo  quot Value exists quot        else         echo  quot Value not found quot

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Below is the simplest and fastest way to determine if a record exists in database or not Good thing is it works in all Relational DB s  SELECT distinct 1 products id FROM products WHERE products id

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I ve used this in the past and it doesn t require a full table scan to see if something exists  It s super fast     UPDATE TableName SET column value WHERE column value IF   ROWCOUNT 0 BEGIN      --Do work END

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Nothing can beat -   SELECT TOP 1 1 FROM products WHERE id    some value     You don t need to count to know if there is a data in table  And don t use alias when not necessary

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For those stumbling upon this from MySQL or Oracle background - MySQL supports the LIMIT clause to select a limited number of records  while Oracle uses ROWNUM

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You can also use   If EXISTS  SELECT 1 FROM dbo T1 WHERE T1 Name  Scot       BEGIN          -- lt Do something gt      END   ELSE          BEGIN        -- lt Do something gt       END

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EXISTS  or NOT EXISTS  is specially designed for checking if something exists and therefore should be  and is  the best option  It will halt on the first row that matches so it does not require a TOP clause and it does not actually select any data so there is no overhead in size of columns  You can safely use SELECT   here - no different than SELECT 1  SELECT NULL or SELECT AnyColumn     you can even use an invalid expression like SELECT 1 0 and it will not break     IF EXISTS  SELECT   FROM Products WHERE id      BEGIN --do what you need if exists END ELSE BEGIN --do what needs to be done if not END

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SELECT CASE WHEN EXISTS  SELECT TOP 1                            FROM dbo  YourTable                            WHERE  YourColumn     YourValue                THEN CAST  1 AS BIT               ELSE CAST  0 AS BIT  END   This approach returns a boolean for you

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SELECT TOP 1 products id FROM products WHERE products id      will outperform all of your suggestions as it will terminate execution after it finds the first record

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Don t think anyone has mentioned it yet  but if you are sure the data won t change underneath you  you may want to also apply the NoLock hint to ensure it is not blocked when reading   SELECT CASE WHEN EXISTS  SELECT 1                       FROM dbo  YourTable  WITH  NOLOCK                       WHERE  YourColumn     YourValue            THEN CAST  1 AS BIT           ELSE CAST  0 AS BIT  END

[sql] Fastest way to determine if record exists

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