SELECT and Column Expressions in SQL

SELECT is how you tell SQL what to compute and what to call the result.

You're already in SQL working on a query. Before running a commission calculation across thousands of deals, you want to verify the formula produces the right number on a known input. SELECT lets you test the arithmetic in isolation — write the expression, give it a label, and SQL evaluates it immediately.

Before you ever touch a table or pull from a database, SELECT already does useful work. You hand it any arithmetic expression — addition, subtraction, multiplication, division — and it hands back a labeled answer. The AS keyword handles the labeling. You write the expression, write AS, then give the column a name:

SQL evaluates the expression and returns one row with one column: commission_amount, value 3600. One query, one result. That's it.

You can return several calculations at once by separating them with commas:

One query, one row, three labeled columns. If someone needs the full breakdown — the deal size, the rate, and the dollar amount — you return all three together.

SELECT works with all four arithmetic operators: +, -, *, and /. Parentheses control the order of operations, exactly like in regular math:

Without the parentheses, SQL multiplies first and you get a different number. With them, the subtraction happens first. Whenever a calculation has multiple steps, parentheses make the order explicit and keep the result from surprising you.

The one thing that trips people up: integer division.

Divide two whole numbers and SQL drops the decimal entirely. 43 / 8 returns 5, not 5.375. Fix it by writing at least one side with a decimal point: 43.0 / 8 returns 5.375000. Any time you need the fractional part of a result, make sure at least one number in the division has a decimal.