Q61. A subquery inside a subquery is called?
A subquery placed inside another subquery is called a **nested subquery** (or multi-level subquery): ```sql SELECT customer_name FROM customers WHERE customer_id IN ( SEL...
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Q62. A subquery that references the outer query?
A **correlated subquery**. It executes once for each row of the outer query. ```sql SELECT * FROM employees e WHERE salary > (SELECT AVG(salary) FROM employees WHERE dept...
Q63. What is the CASE function?
SQL's version of IF-THEN-ELSE. Two forms: simple and searched. ```sql -- Searched CASE (more flexible) SELECT name, CASE WHEN salary >= 100000 THEN 'Executive' WHEN salar...
Q64. Different types of SQL statements?
DDL (CREATE, ALTER, DROP, TRUNCATE), DML (INSERT, UPDATE, DELETE, SELECT), DQL (SELECT — sometimes grouped with DML), DCL (GRANT, REVOKE), TCL (COMMIT, ROLLBACK, SAVEPOIN...
Q65. Which statements are DDL?
**DDL** stands for **Data Definition Language**. DDL statements define, alter, and destroy database schema structures (tables, indexes, views, schemas, constraints): ### ...
Q66. DML includes?
**DML** stands for **Data Manipulation Language**. DML commands manage, insert, retrieve, and modify actual data rows stored inside database tables: ### Core DML Statemen...
Q67. GRANT and REVOKE are under?
`GRANT` and `REVOKE` belong to **DCL (Data Control Language)**. ### Purpose of DCL: DCL commands manage user security privileges, access rights, and permissions across da...
Q68. Which is NOT a DML statement?
Statements such as **`COMMIT`**, **`ROLLBACK`**, **`CREATE`**, **`ALTER`**, and **`DROP`** are **NOT** DML statements: - `COMMIT` and `ROLLBACK` are **TCL (Transaction Co...
Q69. Which statement inserts new data?
The **`INSERT INTO`** statement is used to add new rows of data into a database table: ```sql INSERT INTO Customers (first_name, last_name, email) VALUES ('John', 'Doe', ...
Q70. Must you specify columns when inserting?
No, if you provide values for ALL columns in the exact table order. But **best practice**: always specify columns. It prevents errors when schema changes and is self-docu...