SQL Count
A commonly used aggregate function in SQL is COUNT(). COUNT() returns the number of rows that match the given criteria.
COUNT(*)
If we only want to see how many records are in a table (but not actually view those records), we could use COUNT(*). COUNT(*) returns everything — including null values and duplicates.
SQL statement
Source Table
| IndividualId | FirstName | LastName | UserName |
|---|
| 1 | Fred | Flinstone | freddo |
| 2 | Homer | Simpson | homey |
| 3 | Homer | Brown | notsofamous |
| 4 | Ozzy | Ozzbourne | sabbath |
| 5 | Homer | Gain | noplacelike |
| 6 | Bono | | u2 |
Result
COUNT(column name)
If we want to see how many non-null values are in a given column, we use COUNT(column name) where column name is the name of the column we want to test.
SQL statement
Source Table
| Id | FirstName | LastName | UserName |
|---|
| 1 | Fred | Flinstone | freddo |
| 2 | Homer | Simpson | homey |
| 3 | Homer | Brown | notsofamous |
| 4 | Ozzy | Ozzbourne | sabbath |
| 5 | Homer | Gain | noplacelike |
| 6 | Bono | | u2 |
Result
Combining COUNT & DISTINCT
If we only want to see how many unique names are in the table, we could nest the DISTINCT inside a COUNT function.
SQL statement
Result