Comparison of Methods for determining whether a record exists in MySQL

I have summarized the common methods for determining whether a record exists:

SQL statement: Select count (*) from tablename;

Then read the value of Count (*) to determine whether the record exists. The performance of this method is a waste. We just want to determine whether the record exists, and it is not necessary to check all the records.

The following method is recommended.

SQL statement: select 1 from tablename where Col = Col limit 1;

Then read the number of rows affected by statement execution.

Of course, here limit 1 is very important. This requires MySQL to find a record and it will not be searched down. The number of rows affected by the execution is either 0 or 1, and the performance has improved a lot.

If you are using PDO, you can use rowcount () to easily reach the number of rows affected by the execution.

Some people may read the records queried by SQL statements, and then judge whether the records exist to determine whether the records exist. This method is feasible, but it is still a waste for our requirements. We do not need to query the records, and all performance loss will occur. This is not recommended.