Basic Column Aliasing with AS

basic

HR wants a formatted employee report with readable column names for an internal dashboard

SELECT

employee_id AS emp_id,

first_name AS first,

last_name AS last,

salary AS monthly_salary,

salary * 12 AS annual_salary,

CONCAT(first_name, ' ', last_name) AS full_name

FROM employees

ORDER BY annual_salary DESC;

emp_id | first | last | monthly_salary | annual_salary | full_name

1 | Alice | Chen | 10000 | 120000 | Alice Chen

2 | Bob | Patel | 8500 | 102000 | Bob Patel

3 | Carol | Nguyen | 7200 | 86400 | Carol Nguyen

AS renames columns in output without changing the table. salary * 12 calculates annual salary inline. CONCAT builds full_name. ORDER BY annual_salary uses the SELECT alias — valid because ORDER BY runs after SELECT in execution order.

All

Arithmetic Operator Precedence

basic

Finance team needs discounted totals and tax-inclusive prices, and the formula must respect operator precedence

SELECT

product_name,

unit_price,

quantity,

discount_pct,

-- Wrong without parentheses: discount subtracted AFTER multiplication

unit_price * quantity - discount_pct AS wrong_discount,

-- Correct: discount applied to subtotal

(unit_price * quantity) * (1 - discount_pct) AS discounted_total,

-- Tax applied to discounted amount

(unit_price * quantity) * (1 - discount_pct) * 1.08 AS total_with_tax

FROM order_items;

product_name | unit_price | quantity | discount_pct | wrong_discount | discounted_total | total_with_tax

Laptop | 1200.00 | 2 | 0.10 | 2399.90 | 2160.00 | 2332.80

Keyboard | 80.00 | 5 | 0.05 | 399.95 | 380.00 | 410.40

Without parentheses, * binds tighter than - so discount_pct gets subtracted from the full product — wrong. Parentheses enforce: (1) calculate subtotal, (2) apply discount percentage, (3) apply tax. This is a common production bug in ETL pipelines.

All

Cross-Database String Concatenation

basic