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SQL UPDATE Statement
SQL UPDATE Statement
Learn how to modify existing records in your database using the SQL UPDATE statement. Master the syntax, understand best practices, and see real-world examples.
Understanding SQL UPDATE
The UPDATE statement modifies existing data in a table. You can update one row, many rows, or even all rows — but watch out! A missing WHERE clause can cause unintended mass updates.
Common SQL UPDATE Interview Questions
- How do you update a single row in a table?
- What happens if you omit the WHERE clause?
- How can you update multiple columns at once?
- How do you update data based on values in other tables?
Basic UPDATE Syntax
The WHERE clause determines which rows to update. Without it, all rows will be updated!
Practical UPDATE Examples
Example 1: Update a User's Email
This example shows how to update a user's email address:
Example 2: Update Multiple Columns
You can update multiple columns in a single statement:
Example 3: Update Video Views
Update values based on their current values:
Example 4: Update with Subquery
Use subqueries to update based on data from other tables:
Mass Updates (Use With Caution)
Warning: This affects every row in the table. Always back up your data and consider using a transaction when performing mass updates.
Best Practices for UPDATE
- Always include a
WHEREclause unless you're intentionally updating everything - Preview affected rows first with a
SELECTusing the same condition - Use transactions when updating multiple related tables
- Keep an audit trail of changes when possible
- Consider the impact on related tables and foreign key constraints
Complex UPDATE Examples
Update Based on Interaction Types
Update data based on relationships between tables:
Conditional Updates
Use complex conditions to determine what to update:
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