SQL Constraints

Types of SQL Constraints – NOT NULL – UNIQUE – CHECK – Primary Key – Foreign Key  SQL NOT NULL Constraint. By default, a column can hold NULL value. If we not want to allow NULL or empty value in a column of our table, then we need to place … Continue Reading →

SQL operators

  ALL Syntax ALL [ ( SELECT-Command ) ] Description: ALL is used to select all records of an SELECT statement. Example: SELECT * FROM tkunden WHERE rating > ALL ( SELECT rating FROM tkunden WHERE stadt=’Berlin’ ); Select all customers where rating is biger than the rating of all … Continue Reading →

SQL Concepts

  What is a SQL?  It is Structured Query language. It is a non procedural language and it is a database language. Categories in SQL commands  There are 3 broad categories in SQL commands. They are namely 1.Data Definition language (DDL)  2.Data Manipulation Language (DML)  3.Transaction Control Commands  Under each category there … Continue Reading →