SQL Select Top Clause

The SQL select top clause is used to return the number of records. It is very helpful when we want to fetch the record from a very large table that contains thousands of records.

Example –

Firstly we create a table with name “emp”-

 Select top 2 * from emp

Output - 

SQL Select TOP PERCENT Example -

Select top 50 percent * from emp

Output -

SQL AND & OR operators

The SQL AND & OR operators used to filter the record that is based on one or more condition.

The AND operator used to show the record if both first and second condition are true.

The OR operator used to show the record if either the first condition OR second condition is true.

Example – Firstly we create the table “emp”

 

AND operator Example –

select * from emp where id='1' AND name='sachin'

Output – 

OR operator Example –

select * from emp where id='1' OR name='pramod'

Output – 

                                                               Author - Sachin Pathak

SQL Foreign key Constraint

A Foreign key in one table points to a primary key in another table.

Firstly we create two tables:-

“employee” table: -

E_Id	Name	Address
1	Sachin	Kanpur
2	Amit	Aligarh
3	Sumt	Etah

“Emp” table

Emp_id	dept	E_Id
1	IT	2
2	sales	1

The SQL Foreign key constraint on create table

Create table Emp

(

Emp_id int NOT NULL PRIMARY KEY,

dept varchar (250) NOT NULL,

E_Id int Foreign Key references employee(E_Id)

)

SQL foreign Key constraint on ALTER Table

ALTER Table Emp

Add foreign key (E_Id)

References Employee (E_Id)

Drop a Foreign Key Constraint –

Alter table Emp

Drop contraint E_Id

                                                Author : - Sachin Pathak