SQL Check Constraints

Check Constraints does not allow the values which are not satisfied the given condition. You can apply Check constraints on more than one column in same table. Check constraints allows to enter null values.

Example

 
create table employee
(eid number(3),
ename varchar2(15),
sal number(5) check (sal>50000));

Employee table

In below table you can enter salary more than 50000

emp_id	name	salary
101	Amit	74000
102	Rahul	84000
103	Sultan	54000
104	Gaurav	60000
105	Hitesh	95000

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Introduction of SQL

Introduction of SQL SQL (Structure Query Language) was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce in the early 1970s. This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasi-relational database management system. Features of SQL SQL is not a case sensitive language. Every commands in SQL should ends with semicolon(;). SQL can also called as sequel (SEQUEL). SQL Sub Language SQL is mainly divided into four sub language Data Definition Language(DDL) Data Manipulation Language(DML) Transaction Control Language(TCL) Data Control Language(DCL) Only for remember You can remember all these command like below; DDL Commands "dr. cat" d-Drop, r-Rename, c-Create, a-Alter, t-Truncate. DML commands "sudi". s-Select, u-Update, d-Delete, i-Insert.

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