Counting Rows

The COUNT() function in SQL is used to return the number of rows that match a specified condition.

Use Case #1: Count the number of rows in a table

SELECT COUNT(*) FROM table_name;

We are running the COUNT() function on all our attributes from a given table. This will count the number of rows.

We can also just target specific column by providing a column_name instead of *

SELECT COUNT(col_name) FROM table_name;

Use Case #2: Counting the number of records that match a condition

A more useful use of counting would be to see how many rows will match a certain condition

SELECT COUNT(*) FROM table_name WHERE condition;

By using the WHERE clause with COUNT, we can select more meaningful data when required.

Use Case #3: Counting the distinct values that populates an attribute

In a scenario where an attribute can have repeating values per records (example: product type sold), it is beneficial to count the number distinct values within that attribute

SELECT COUNT(DISTINCT column_name) FROM table_name;

In the SQL query above, we are using the DISTINCT keyword to not counting repeating values