SQL

Which command is used t o add new row in a table?

Answer explanation

insert

syntax of this command is

insert into <table name> values <(val1, val2,......);

ex:

insert into emp values( 1, 'Harry, 10000);

Which command is used to change the schema of the the table?

Answer explanation

alter table <table name> [add] [modify][change][drop] <col. description>;

Which command is used to change the values of columns in SQL?

Answer explanation

update command

syntax:

update <table name> set <column name> = <value>, <col-name>=<value>,..... where <condition>;

A table customer contains 5 rows and 7 columns. what will be its caardinality and degree?

Answer explanation

Degree: Number of attributes

Cardinality: Number of rows

degree 7, Cardinality 5

What is Primary key?

Answer explanation

A column or a set of columns which can uniquely identify a row in a relation. Primary key cannot have Null values

Define foreign key?

Answer explanation

it is a collumn that references the primary key of another table.

Write two differences between DDL and DML commands of SQL.

Answer explanation

DDL STAND FOR DATA DEFINATION LANGUAGE

DML STAND FOR DATA MANIPULATION LANGUAGE

DDL USED TO CREATE, MODIFY OR DELETE STRUCTURE OF THE TABLE

DML UED TO MANIPULATE RECORDS OF THE TABLE

Write the difference between CHAR and VARCHAR.

Answer explanation

CHAR FIXED LENGTH STRING

VARCHAR IS VARIABLE LENGTH STRING

CHAR STRINGS ARE RIGHT PADDED WITH SPACES TO THE SPECIFIED LENGTH

VARCHAR STRINGS ARE NOT RIGHT PADDED WITH SPACES. THE LENGTH IS ACTUAL DATA IT CONTAINS.

What do you mean by NULL?

A table item and store have one common column item-id. item table consists of 5 rows and 3 coluns while the store table consists of 7 towns and 5 columns. What will be the degree and cardinality of these tables in the cartisian product?

Answer explanation

Degree 8 ( 5 + 3)

carinality 35 ( 7 x 5)