Introduction to SQL

Structured Query Language SQL

SQL (Structured Query Language) is a query language for relational databases. The roots of SQL go back to SQUARE, a more mathematical oriented language and SEQUEL, a predecessor of SQL from the seventies. There exist different standards (ISO and ANSI) of SQL, but the most common one is SQL-92. The latest standard SQL-99 (or SQL3) even includes XML. In the following Units we will give a simple overview of the most important SQL functions.

remark This lesson is geared to the SQL-99 standard (GULUTZAN et al. 1999). However, this standard is not implemented by all database systems constantly. For example, some commands are named differently or their syntax is constructed differently. For this reason, SQL commands from this lesson might not work in certain systems. If you encounter problems, please check in the respective user manuals whether or not the command is supported at all, whether it is named, or constructed differently. Most database systems also go beyond the standard. However, caution is advised with these SQL extensions since they can vary considerably from system to system.

Learning Objectives

  • You understand the basic SQL concepts and are able to explain the use of SQL in the areas of data definition, data manipulation, and data control.
  • You are able to use SQL to create, modify, and delete tables.
  • You can express simple and complex queries with the help of SQL and know how SQL queries are used in nesting or in combinations. You are also able to correctly apply arithmetic operators and set operators within SQL queries.
  • You master SQL to add, modify, and delete data tuples.

SQL overview

SQL Concept

Data Definition(DDL)

Data Manipulation(DML)

Data Control (DCL)