DB - Count(*) vs count(1) vs count(column_name)

In general, count function accepts only one argument and counts the number of rows.

Example table:

Office with 5 employees:

Id name

1 ram

2 sham

3 jadu

4 madhu

5 NULL

>>>>>>>>>>count(*)<<<<<<<<<<

1. Count(*): when * is used as an argument, it simply counts the total number of rows including the NULLs.

Query: Select count(*) as total from office

Output: Total: 5

>>>>>>>>>>count(1)<<<<<<<<<<

2. Count(1): it counts all the rows including NULLs. What count(1) really does is that it replaces all the records we get from the query result with the value 1 and then counts the rows.

Query: Select 1 from office

Output:

1

1

1

1

1

Query: Select count(1) as total from office

Output: total: 5

>>>>>>>>>>count(column_name)<<<<<<<<<<

3. Count(column_name): it counts all the rows but not NULLs.

Query: Select count(id) as total from office

Output: 5

Query: Select count(name) as total from office

Output: 4