Because there are several different database vendors, there are a set of standards that must exist across the database platforms. ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) and they came up with the set of standards that indicate how the SQL Language should be used. This standard allows us to use the same queries in each of the relational databases on the market. Each vendor, however, can come up with their own SQL statements for their databases to assist the data professional, but these SQL statements are considered proprietary and may need to be changed before the query can be run on a different vendor’s database system. The standard that most database systems follow is called SQL-92. The 92 stands for 1992.
Yikes! I wasn’t even out of high school then and my kids tell me I am an old geezer now. There are now many differences between database vendors and their SQL implementations. This books seeks to introduce the basic features, which are part of the SQL-92 database standard.