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.

The Data Definition Language (DDL) is used to manage table and index structure.
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..