Q91. Delete column CITY from ADDRESSES?
To remove a column from an existing table schema, use `ALTER TABLE ... DROP COLUMN`: ```sql ALTER TABLE addresses DROP COLUMN city; ``` *Production Warning:* Dropping a c...
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Q92. What are Indexes?
Data structures (typically B-Trees) that speed up data retrieval at the cost of slower writes and extra storage. Think of them as a book's table of contents.
Q93. Clustered vs Non-Clustered?
- **Clustered**: Determines physical storage order. One per table. The data IS the index. - **Non-Clustered**: Separate structure with pointers to data. Multiple allowed ...
Q94. Statement for assigning privileges?
`GRANT`. To remove: `REVOKE`. ```sql GRANT SELECT, INSERT ON database.orders TO 'app_user'@'%'; REVOKE DELETE ON database.orders FROM 'app_user'@'%'; ```
Q95. Types of privileges?
1. **System privileges**: CREATE, DROP, ALTER (database-level) 2. **Object privileges**: SELECT, INSERT, UPDATE, DELETE, EXECUTE (table/procedure-level)
Q96. Privileges a user can grant?
In SQL security management, database administrators can grant specific privileges using the `GRANT` statement: - **Data Manipulation Privileges**: `SELECT`, `INSERT`, `UP...
Q97. What is SQL Injection?
A code injection attack where malicious SQL is inserted via user input. Prevention: 1. **Parameterized queries** (prepared statements) 2. **Input validation** 3. **ORM fr...
Q98. What does "locking" refer to?
A mechanism to prevent concurrent transactions from interfering with each other. Locks can be **shared** (read locks, multiple allowed) or **exclusive** (write locks, onl...
Q99. Main transaction controls?
- `COMMIT` — Make changes permanent - `ROLLBACK` — Undo all changes in the transaction - `SAVEPOINT` — Set a partial rollback point ```sql START TRANSACTION; UPDATE accou...
Q100. A transaction that completes execution is said to be?
A database transaction that finishes all operations successfully and persists its changes permanently to durable storage is said to be **Committed**: ```sql START TRANSAC...