In T-SQL, COUNT returns the number of items in a group. COUNT works like the COUNT_BIG function. The only difference between the two functions is their return values. COUNT always returns an int data type value. COUNT_BIG always returns a bigint data type value. COUNT(*) returns the number of items in a group. This includes NULL values and duplicates.
The Microsoft Press book T-SQL Querying by Ikzik Ben-Gan et al has an example table called Orders that you could use in a non-production server. We could use this table to illustrate the basics of COUNT. The script below creates the table and populates it with a bit of data.
