SQL Default Constraints

Default Constraints is used to insert a default value into a column. The default value will be added to all new records, if no other value is specified.

My SQL or SQL Server or Oracle or MS Access

 
create table Employee
(
e_id number(3) NOT NULL,,
e_name varchar(15),
sal number(5),
City varchar(255) DEFAULT 'Delhi',
);

In above syntax in city column by default value for city of every employee is delhi.

SQL DEFAULT Constraint on Alter Table

My SQL

 
ALTER TABLE Employee
ALTER City SET DEFAULT 'delhi'

SQL Server or MS Access

 
ALTER TABLE Employee
ALTER COLUMN City SET DEFAULT 'delhi'

Oracle

 
ALTER TABLE Employee
ALTER City SET DEFAULT 'delhi'

Drop Default Constraints

My SQL

 
ALTER TABLE Employee
ALTER City DROP DEFAULT

SQL Server or Oracle or MS Access

 
ALTER TABLE Employee
ALTER COLUMN City DROP DEFAULT

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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.

SQL Syntax

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DDL Commands in SQL

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