This chapter provides an overview of how to use SQL to perform simple operations. This tutorial is only intended to give you an introduction and is in no way a complete tutorial on SQL. Numerous books have been written on SQL, including [melt93] and [date97]. You should be aware that some PostgreSQL language features are extensions to the standard.
In the examples that follow, we assume that you have created a database named mydb, as described in the previous chapter, and have been able to start psql.
Examples in this manual can also be found in the PostgreSQL source distribution in the directory src/tutorial/. (Binary distributions of PostgreSQL might not provide those files.) To use those files, first change to that directory and run make:
$ cd …/src/tutorial
$ make
This creates the scripts and compiles the C files containing user-defined functions and types. Then, to start the tutorial, do the following:
$ psql -s mydb
…
mydb=> \i basics.sql
The \i command reads in commands from the specified file. psql’s -s option puts you in single step mode which pauses before sending each statement to the server. The commands used in this section are in the file basics.sql.
Concepts
PostgreSQL is a relational database management system (RDBMS). That means it is a system for managing data stored in relations. Relation is essentially a mathematical term for table. The notion of storing data in tables is so commonplace today that it might seem inherently obvious, but there are a number of other ways of organizing databases. Files and directories on Unix-like operating systems form an example of a hierarchical database. A more modern development is the object-oriented database.
Each table is a named collection of rows. Each row of a given table has the same set of named columns, and each column is of a specific data type. Whereas columns have a fixed order in each row, it is important to remember that SQL does not guarantee the order of the rows within the table in any way (although they can be explicitly sorted for display).
Tables are grouped into databases, and a collection of databases managed by a single PostgreSQL server instance constitutes a database cluster.
