SQL

SQL Remove NOT NULL Constraint

#SQL Server

ALTER TABLE Customers
ALTER COLUMN age INT;

#Oracle

ALTER TABLE Customers
MODIFY (age NULL);

#MySQL

ALTER TABLE Customers
MODIFY age INT;

#PostgreSQL

ALTER TABLE Customer
ALTER COLUMN age DROP NOT NULL;

SQL NOT NULL Constraint

CREATE TABLE Colleges (
  college_id INT NOT NULL,
  college_code VARCHAR(20),
  college_name VARCHAR(50)
);

SQL NOT NULL Constraint

CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255) NOT NULL,
    Age int
);

SQL NOT NULL Constraint

CREATE TABLE Colleges (
  college_id INT NOT NULL,
  college_code VARCHAR(20) NOT NULL,
  college_name VARCHAR(50)
);