constraint sql code example

Example 1: how to remove foreign key constraint in sql

USE AdventureWorks2012;  
GO  
ALTER TABLE dbo.DocExe   
DROP CONSTRAINT FK_Column_B;   
GO

Example 2: sql constraints

NOT NULL 	 # Ensures a column cannot have a NULL value
UNIQUE 		 # Ensures all values in a column are unique
PRIMARY KEY  # Identifies a record in a table, is NOT NULL & UNIQUE
FOREIGN KEY  # References a unique record from another table
CHECK		 # Ensures all column values satisfy a condition
DEFAULT		 # Set a default value for a column if none is entered
INDEX		 # Quick way of retrieving records from database

Example 3: constraint sql

create table etc(
  numeric (4) anything constraint Gives_name_to_a_restriction primary key);

Example 4: constraints in sql

# The most common constraints are
NOT NULL 	 # Ensures a column cannot have a NULL value
UNIQUE 		 # Ensures all values in a column are unique
PRIMARY KEY  # Identifies a record in a table, is NOT NULL & UNIQUE
FOREIGN KEY  # References a unique record from another table
CHECK		 # Ensures all column values satisfy a condition
DEFAULT		 # Set a default value for a column if none is entered
INDEX		 # Quick way of retrieving records from database

Example 5: sql constarint

It creates a new constraint on an existing table, which is used to specify
rules for any data in the table.
Example: Adds a new PRIMARY KEY constraint named ‘user’ on columns
ID and SURNAME.
ALTER TABLE users
ADD CONSTRAINT user PRIMARY KEY (ID, SURNAME);

Example 6: constraint

print("hello world");
alert(print);