Although there is an ANSI standard for SQL, each database vendor implements SQL with their own variations and enhancements to the standard as well as missing elements from the standard. This creates some degree of confusion. In most cases, their implementation exactly matches the standard, but they have taken different approaches as to how their database was constructed.

Some high-priced databases are Microsoft SQL Server, IBM’s DB2, Oracle, Informix, and Sybase. Others are open source versions such as MySQL, SAP, and PostgresSQL.

We will attempt to highlight these differences with notes, tips, and examples, so that the SQL should execute properly on the platform of your choice. In most cases, SQL is very portable from database to database, regardless of the vendor’s implementation.