Core Code
Core Code Modern Dev Handbook

SQL Where

The WHERE clause filters records based on conditions. Learn comparison operators, text filters, numeric filters, and safe handling of NULL values.
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SQL WHERE Clause

The WHERE clause is used to filter records. It lets you return only the rows that match a specific condition.

WHERE Syntax

SELECT column1, column2, ...
FROM table_name
WHERE condition;

Example: Filter by Exact Match

Return customers from a specific country:

SELECT name, country
FROM customers
WHERE country = 'USA';

Comparison Operators

WHERE conditions commonly use these operators:

  • = equal
  • <> or != not equal
  • > greater than
  • < less than
  • >= greater than or equal
  • <= less than or equal

Example: Numeric Comparison

Return products with price greater than 100:

SELECT name, price
FROM products
WHERE price > 100;

Example: Date Comparison

Return orders placed after a specific date:

SELECT id, order_date
FROM orders
WHERE order_date > '2026-01-01';

Text Values and Quotes

Text values are usually written in single quotes. If your text contains a single quote, you must escape it (database-specific) or use safe parameter binding in your application code.

SELECT name
FROM customers
WHERE city = 'Istanbul';

Filtering with Multiple Conditions

You can combine conditions using AND / OR / NOT. These operators are covered in dedicated lessons, but here is the basic idea:

SELECT name, country, status
FROM customers
WHERE country = 'USA' AND status = 'active';

Use parentheses when combining multiple conditions to make the logic clear:

SELECT name, country, status
FROM customers
WHERE country = 'USA' AND (status = 'active' OR status = 'trial');

Filtering NULL Values

NULL means “no value”. You cannot compare NULL using = or !=. Use IS NULL or IS NOT NULL instead.

SELECT name, phone
FROM customers
WHERE phone IS NULL;
SELECT name, phone
FROM customers
WHERE phone IS NOT NULL;

Common WHERE Patterns

These patterns are covered in detail in later lessons, but you will see them often:

  • IN for matching a list of values
  • BETWEEN for matching a range
  • LIKE for pattern matching
SELECT name, country
FROM customers
WHERE country IN ('USA', 'Canada');
SELECT name, price
FROM products
WHERE price BETWEEN 50 AND 100;
SELECT name
FROM customers
WHERE name LIKE 'A%';

Common Mistakes

  • Forgetting quotes around text values
  • Comparing NULL using = instead of IS NULL
  • Mixing AND and OR without parentheses

Next Steps

Continue with SQL ORDER BY to sort your filtered results, then move on to AND / OR / NOT for more complex filtering logic.

SQL Order By →