SQL

SQL provides several commands to manipulate data:

• SELECT: Retrieve data from the database.
• INSERT: Add new rows to a table.
• UPDATE: Modify the values of existing rows.
• DELETE: Remove rows from a table.

Aggregate Functions

SQL includes aggregate functions that operate on all the values in a column:

• COUNT: Counts the number of values.
• SUM: Calculates the total sum of values.
• AVG: Computes the average of the values.
• MAX: Finds the highest value.
• MIN: Finds the lowest value.

You can use the DISTINCT keyword before the argument to exclude duplicate values before applying the function.

Special Case: COUNT(*)

• COUNT(*) counts all rows in a table, including those with NULL values.
• Other forms of COUNT (e.g. COUNT(column_name)) ignore NULL values.