Q11. Valid constraints in MySQL?
MySQL supports a complete set of integrity constraints: 1. **`PRIMARY KEY`**: Uniquely identifies each row (implies `NOT NULL` and `UNIQUE`). 2. **`FOREIGN KEY`**: Enforc...
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Q12. Rename column Address to Addr in Customer?
```sql -- MySQL ALTER TABLE Customer CHANGE Address Addr VARCHAR(50); -- PostgreSQL / Standard ALTER TABLE Customer RENAME COLUMN Address TO Addr; ```
Q13. What if autocommit is enabled?
Every individual statement is automatically committed. In MySQL, autocommit is ON by default. Turn it off for multi-statement transactions: ```sql SET autocommit = 0; -- ...
Q14. Default isolation level in MySQL?
**REPEATABLE READ** (InnoDB engine). Prevents dirty reads and non-repeatable reads, but phantom reads are possible (though InnoDB uses MVCC + gap locking to mostly preven...
Q15. Is autocommit enabled by default in MySQL?
**Yes**, in MySQL (using the standard InnoDB storage engine), **autocommit is enabled by default** (`autocommit = 1`): ### What Autocommit Means: - Every individual SQL s...
Q16. What is a virtual table in MySQL?
In MySQL and relational databases, a **virtual table** is called a **View**: ```sql CREATE VIEW active_customer_summary AS SELECT id, first_name, last_name, email FROM Cu...