SQL MCQ Questions and answers

SQL (Structured Query Language) is a special-purpose programming language designed for managing data held in a relational database management system (RDBMS).
Originally based upon relational algebra and tuple relational calculus, SQL consists of a data definition language and a data manipulation language. The scope of SQL includes data insert, query, update and delete, schema creation and modification, and data access control.

Data Definition Language, represented by DDL, is the subset of SQL commands used to manipulate Oracle Database structures, including tables. DDL commands are responsible for defining, modifying, and deleting the structure of a database, such as creating and altering tables, defining constraints, and managing indexes. They do not deal with the actual data within the tables, which is the primary function of Data Manipulation Language (DML) commands. So, Option A is the correct answer.

CREATE, ALTER, RENAME, DROP and TRUNCATE statements are the names of few data definition elements.

LIKE is a keyword that is used in the WHERE clause. Basically, LIKE allows us to do a search based operation on a pattern rather than specifying exactly what is desired (as in IN) or spell out a range (as in BETWEEN).

The syntax is as follows:
SELECT "column_name"
FROM "table_name"
WHERE "column_name" LIKE {PATTERN}

{PATTERN} often consists of wildcards. In SQL, there are two wildcards:

• 1=% (percent sign) represents zero, one, or more characters.
• 2=_ (underscore) represents exactly one character.

Always use IS NULL to look for NULL values.

Syntax:

SELECT "column_name"
FROM "table_name"
WHERE "column_name" IS NULL

To change the structure of the table we use ALTER TABLE.
Sytax:
ALTER TABLE "table_name"
ADD "column_name" datatype

OR

ALTER TABLE "table_name"
DROP COLUMN "column_name"
etc..

RENAME: - With RENAME statement you can rename a table.
REVOKE: - The REVOKE command removes user access rights or privileges to the database objects.
GRANT: - In SQL GRANT is a command used to provide access or privileges on the database objects to the users.
UPDATE: - The UPDATE Statement is used to modify the existing rows in a table.

RENAME, REVOKE and GRANT are DDL(Data Definition Language) commands and UPDATE is DML(Data Manipulation Language) command.

The SELECT keyword allows us to grab all information from a column (or columns) on a table. This, of course, necessarily means that there will be redundancies. What if we only want to select each distinct element? This is easy way to accomplish in SQL. All we need to do is that to add DISTINCT after SELECT. The syntax is as follows:

SELECT DISTINCT column_name
FROM table_name;

Sometimes we need to change the data type of a column. To do this, we use the ALTER TABLE Modify Column command.
Sytax:
ALTER TABLE table_name
MODIFY column_name "New Data Type"

Correct order of SELECT, FROM and WHERE clause is as follow:
SELECT column_name1, column_name2, ....
FROM table_name
WHERE condition

So, only
SELECT Username, Password FROM Users
follows the above syntax.

The FROM SQL clause is used to specify from which table we are selecting or deleting data. It defines the source table from which data will be retrieved or modified in a SQL query. Here's the breakdown:

Option A: specify what table we are selecting or deleting data FROM
This option correctly describes the purpose of the FROM clause, which is to specify the table from which data operations will be performed.

Option B: specify range for search condition
This is not the primary purpose of the FROM clause. It is used for table specification, not defining search ranges.

Option C: specify search condition
The FROM clause is not used to specify search conditions. Search conditions are typically defined in the WHERE clause.

Option D: None of these
Option A is a valid description of the FROM clause's purpose.

So, the correct answer is Option A: specify what table we are selecting or deleting data FROM.