SQL WHERE Function
Quick summary: The SQL WHERE clause filters rows based on conditions.
SQL WHERE Syntax
SELECT column1 FROM table_name WHERE conditionSQL
SQL WHERE Basic examples
SELECT * FROM users WHERE id = 5;SQL
Output:
Single user rowFilters rows by exact match.
SQL WHERE Real-world usage
SELECT * FROM orders WHERE status = 'paid';SQL
Output:
Paid orders onlyFilters business-specific data.
SQL WHERE Edge cases
SELECT * FROM users WHERE deleted_at IS NULL;SQL
Output:
Non-deleted usersHandles NULL values correctly.
SQL WHERE Common mistakes
Using = NULL
NULL must be checked with IS NULL.
Incorrect
WHERE deleted_at = NULLCorrect
WHERE deleted_at IS NULLUse IS NULL or IS NOT NULL.
SQL WHERE Frequently Asked Questions
What does SQL WHERE do?
Filters rows based on conditions.
Use case of WHERE?
Selecting specific records.
Can WHERE use multiple conditions?
Yes, with AND/OR.
Supports operators?
Yes (=, >, <, LIKE, IN, etc).
Common mistake?
Forgetting WHERE in DELETE/UPDATE.
Can WHERE use functions?
Yes.
Performance impact?
Depends on indexes.
Difference from HAVING?
WHERE filters before aggregation.
Supports subqueries?
Yes.
Case sensitivity?
Depends on DB collation.
Best practice?
Use indexed columns.
Used with SELECT?
Yes.