What is the most efficient way to check the presence of a row in a MySQL table?

The most efficient want to check the presence of a row, use the count():

select count(1) from yourTableName where yourCondition;

Let us first create a table:

mysql> create table DemoTable (    Id int,    FirstName varchar(20) ); Query OK, 0 rows affected (0.73 sec)

Following is the query to insert some records in the table using insert command:

mysql> insert into DemoTable values(100,'Larry'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(110,'Sam'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(120,'Mike'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values(130,'Carol'); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable values(140,'David'); Query OK, 1 row affected (0.12 sec)

Following is the query to display records from the table using select command:

mysql> select *from DemoTable;

This will produce the following output

+------+-----------+ | Id | FirstName | +------+-----------+ | 100 | Larry | | 110 | Sam | | 120 | Mike | | 130 | Carol | | 140 | David | +------+-----------+ 5 rows in set (0.00 sec)

Following is the query to check the presence of a row in a table. Here, we are checking for row with Id = 130:

mysql> select count(1) from DemoTable where Id=130;

This will produce the following output:

+----------+ | count(1) | +----------+ | 1 | +----------+ 1 row in set (0.00 sec)

The above output tells that row is present.

NOTE: If you get 1 that means row is present otherwise the row isn’t present.