What Is the Difference Between count(*) and count(column)?

Answer: The count() function is an aggregate function used to calculate the number of rows. The differences are as follows:

• count(*) collects statistics on the number of rows in all columns. Data whose value is NULL is not ignored during statistics collection.
• count(column) contains only the column name column. Data whose value is NULL is ignored during statistics collection.

-- Create a table and insert data into the table.
gaussdb=# CREATE TABLE test(c1 int);
gaussdb=# INSERT INTO test VALUES(1),(2),(3);
gaussdb=# INSERT INTO test VALUES(NULL);

--count(*) counts the number of rows and does not ignore the data whose value is NULL.
gaussdb=# SELECT count(*) FROM test;
 count 
-------
     4
(1 row)

--count(column) counts the number of rows and does not ignore the data whose value is NULL.
gaussdb=# SELECT count(c1) from test;
 count 
-------
     3
(1 row)

-- Delete.
gaussdb=# DROP TABLE test;