What does “select count(1) from table_name” on any database tables mean?

Question

When we execute select count(*) from table_name it returns the number of rows.

What does count(1) do? What does 1 signify here

Answer 1

SELECT COUNT(1) from 
should do the exact same thing as 
SELECT COUNT(*)  from 
There may have been or still be some reasons why it would perform better than SELECT COUNT(*)on some database, but I would consider that a bug in the DB.
SELECT COUNT(col_name) from 
however has a different meaning, as it counts only the rows with a non-null value for the given column.

                                                        

              
                
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