Fixing Common SQL Errors

SQL errors can disrupt your database operations, but most issues are straightforward to resolve. Here are some frequent problems you might encounter:

1. Syntax Errors
🔐 Error: Syntax error near ‘FROM’

🔨Fix: Check SQL syntax, including missing commas, incorrect keywords, and misplaced parentheses. Example:
— Correct syntax
SELECT name, age FROM users;
— Incorrect syntax (missing comma between columns)
SELECT name age FROM users;

2. Column or Table Not Found
🔐Error: Unknown column ‘username’ in ‘field list’

🔨Fix: Verify table and column names exist. Use
SHOW COLUMNS FROM table_name;

3. Incorrect Data Types
🔐Data truncated for column ‘age’

🔨Fix: Ensure data matches the column type. Example:
ALTER TABLE users MODIFY age INT;

4. Division by Zero
🔐Error: Error: Division by 0

🔨Fix: Use NULLIF() to prevent division by zero.
SELECT value/NULLIF(divisor, 0) FROM table;

5. NULL Value Errors
🔐Error: Column ’email’ cannot be null

🔨Fix: Use IS NOT NULL constraint or handle NULL values properly.

6. Primary Key Duplication
🔐Error: Duplicate entry for key PRIMARY

🔨Fix: Ensure unique values or use ON DUPLICATE KEY UPDATE.

7. Foreign Key Constraint Failures
🔐Error: Cannot add or update child row

🔨Fix: Ensure referenced values exist in the parent table.

8. Deadlocks & Lock Timeout
🔐Error: Lock wait timeout exceeded

🔨Fix: Optimize queries and indexes, use transactions properly.

By addressing these common errors, you can write efficient and error-free SQL queries

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