Question

In my SQL query I just need to check whether data exists for a particular userid.

I always only want one row that will be returned when data exist.

I have two options

1. select count(columnname) from table where userid=:userid

2. select count(1) from tablename where userid=:userid

I am thinking second one is the one I should use because it may have a better response time as compared with first one.

Answer 1

There can be differences between count(*) and count(column). count(*) is often fastest for reasons discussed here. Basically, with count(column) the database has to check if column is null or not in each row. With count(column) it just returns the total number of rows in the table which is probably has on hand. The exact details may depend on the database and the version of the database.

Short answer: use count(*) or count(1). Hell, forget the count and select userid.

You should also make sure the where clause is performing well and that its using an index. Look into EXPLAIN.