SQL Interview: 81 COUNT(*) and COUNT(Column)

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Development Level: Medium

Question:

You execute the following code:

DROP TABLE IF EXISTS dbo.Table1;
GO

CREATE TABLE dbo.Table1
(
    Column1 int NULL
);
GO

INSERT dbo.Table1 (Column1)
VALUES (1), (NULL), (NULL), (2);
GO

-- Query 1
SELECT COUNT(*), COUNT(Column1)
FROM dbo.Table1;

-- Query 2
SELECT COUNT(*), COUNT(Column1)
FROM dbo.Table1
WHERE Column1 = NULL;