SQL Comments & Operators

Annotate queries and calculate values.

✍️ 3 exercises + code challenge in this lesson

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SQL Comments

Single line: -- comment
Multi-line: /* comment */

SQL Operators

Arithmetic: + - * / %
Comparison: = <> > < >= <=
Logical: AND OR NOT BETWEEN IN LIKE EXISTS IS NULL
String joining: || (standard, PostgreSQL, SQLite) or CONCAT() (MySQL, SQL Server)

Key Takeaways: SQL Comments & Operators

Mastering SQL Comments & Operators helps you write clean and reliable SQL code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

SQL Comments & Operators Code Example

SQL

/* Price list with tax and discount */
SELECT ProductName,
       Price,
       Price * 0.18           AS Tax,      -- 18% sales tax
       Price * 1.18           AS WithTax,
       Stock % 2 = 0          AS EvenStock,
       'Item: ' || ProductName AS Label
FROM Products;

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SQL Comments & Operators Practice Exercises

Check what you learned in “SQL Comments & Operators”.

/ 3 solved

Fill in the blank

Write a single-line SQL comment.

 this query lists products
SELECT * FROM Products;

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Multiple choice

Which operator joins strings in standard SQL and SQLite?

|| + & .

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Code challenge

Select ProductName || ' (' || Category || ')' AS Label for ProductID 2.

Write the code in the live editor. Your answer is checked automatically.

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SQL INSERT INTO SELECT

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SQL CREATE DATABASE

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