SQL OPERATORS

What are SQL operators and when should I use each type?

SQL operators perform arithmetic, comparison, logical, string, bitwise, and set operations on one or more expressions.

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Compatible dialects for SQL OPERATORS: PostgreSQL, MySQL, MariaDB, SQL Server, Oracle, SQLite, Snowflake, BigQuery, Redshift, and all ANSI-compliant databases support the core operator set. Certain operators (%, bitwise, REGEXP) vary by dialect.

SQL OPERATORS Full Explanation

SQL operators are special symbols or reserved words that evaluate to a value when placed between or in front of expressions. They are the building blocks of predicates, calculations, and control flow inside queries. Operators are grouped into categories:1. Arithmetic: + - * / % perform mathematical calculations on numeric data types.2. Comparison: = <> != ><>= <= IS IS NOT compare two values and return TRUE, FALSE, or UNKNOWN.3. Logical: AND OR NOT combine multiple boolean expressions into a single truth value.4. String/Concatenation: || (ANSI) or + (SQL Server) joins two strings.5. Bitwise: & | ^ ~ operate at the bit level (dialect specific).6. Set operators: UNION UNION ALL INTERSECT EXCEPT merge result sets while enforcing set logic.7. Other specialized operators include LIKE, BETWEEN, IN, ANY, ALL, SOME, and pattern-matching REGEXP/LRLIKE depending on dialect.Operator precedence determines evaluation order (e.g., * and / before + and -; NOT before AND before OR). Parentheses override precedence. NULLs propagate through arithmetic and comparison operators and yield UNKNOWN in boolean logic unless the operator explicitly treats NULL (e.g., IS NULL).

SQL OPERATORS Syntax

-- Generic operator usage pattern
SELECT expression1 operator expression2;

-- Multiple operators with precedence
SELECT (salary + bonus) * tax_rate AS tax_due
FROM employees;

SQL OPERATORS Parameters

Example Queries Using SQL OPERATORS

-- Arithmetic
SELECT 10 + 5 AS sum, 10 % 3 AS modulus;

-- Comparison and logical
SELECT *
FROM orders
WHERE status = 'shipped' AND shipped_at >= CURRENT_DATE - INTERVAL '7' DAY;

-- String concatenation (ANSI)
SELECT first_name || ' ' || last_name AS full_name
FROM users;

-- Bitwise (PostgreSQL & MySQL)
SELECT permissions & 4 AS can_write
FROM roles;

-- Set operator
SELECT id, email FROM users_active
UNION
SELECT id, email FROM users_trial;

Expected Output Using SQL OPERATORS

Arithmetic query returns two scalar columns (sum and modulus)
Comparison query filters orders to the last 7 days of shipped status
Concatenation query outputs full_name for each user
Bitwise query shows integer result of bit mask
UNION query returns a deduplicated list of id and email across two tables

Use Cases with SQL OPERATORS

Calculating totals, averages, or derived metrics with arithmetic operators.
Filtering rows based on comparisons and boolean logic.
Building dynamic text fields such as full names or URLs.
Implementing permission checks with bit masks.
Combining results from multiple tables or subqueries into one canonical set.

Common Mistakes with SQL OPERATORS

Forgetting operator precedence and getting unexpected results; always use parentheses for clarity.
Using = instead of IS when comparing to NULL (col IS NULL, not col = NULL).
Mixing dialect specific string concatenation operators (+ vs ||) without checking compatibility.
Assuming UNION keeps duplicates (it removes them; use UNION ALL when duplicates are acceptable).
Misinterpreting UNKNOWN result from NULL comparisons inside WHERE clauses.

First Introduced In

SQL-86 (first ANSI SQL standard)

Frequently Asked Questions

What is the difference between UNION and UNION ALL?

UNION removes duplicate rows after combining result sets, whereas UNION ALL keeps duplicates and is therefore faster because it skips the distinct step.

How does operator precedence work in SQL?

The database evaluates expressions in a fixed order: parentheses first, arithmetic (*, /, %), arithmetic (+, -), comparison, NOT, AND, OR. Parentheses can override the default sequence.

Can I use operators on NULL values?

You can, but arithmetic and comparison operators generally propagate NULL, returning NULL or UNKNOWN. Use COALESCE to replace NULLs or IS NULL for comparisons.

Are bitwise operators portable across databases?

No. Bitwise operators (&, |, ^, ~) are supported in PostgreSQL, SQL Server, MySQL, and MariaDB, but not in standard SQLite or Oracle without extensions.