8.5. Crash Course in SQL

If you want to work with databases, you must learn to speak their language. Databases speak Structured Query Language, better known as SQL, which was invented by E. F. Codd in the 1970s. Instead of working with tables one record at a time, SQL manages groups of records as a single entity, which makes it suitable for creating queries of any complexity. This language has been standardized, and now most database servers, and ADO itself, accept its ANSI-92 dialect.

SQL encompasses two distinct categories of statements: data definition language (DDL) and data manipulation language (DML). The DDL subset includes a group of statements that allow you to create database structures, such as tables, fields, indices, and so on. The DML subset includes all the commands that allow you to query and modify the data in the database, add new records, or delete existing ones. While both subsets are equally important, most of the time you'll use only DML statements to retrieve and update data stored in a database whose structure has been already defined in advance (possibly by another developer or the database administrator). For this reason, I focus in this section exclusively on the DML subset of the language. You need the information contained in this section to build queries that can't be created interactively using the SQL Query Builder (which permits you to create only the simplest queries).