Web server info - CHAPTER 28 FROM DATABASES TO DATATYPES with
CHAPTER 28 FROM DATABASES TO DATATYPES with the number passed into setval rather than the next value in the sequence. For example, if passed in with a value of 2112 and is_called set to FALSE, calling nextval will first return 2112 and then increase from there. Deleting a Sequence To delete a sequence, simply use the DROP SEQUENCE command: DROP SEQUENCE name [, …] [ CASCADE | RESTRICT ] The DROP SEQUENCE command allows you to enter one or more sequence names to be dropped in a given command. The CASCADE and RESTRICTkeywords function just like with other objects; if CASCADEis specified, any dependent objects will be dropped automatically; if RESTRICTis specified, PostgreSQL will refuse to drop the sequence. Datatypes and Attributes It makes sense that you would want to wield some level of control over the data placed into each column of a PostgreSQL table. For example, you might want to make sure that the value doesn t surpass a maximum limit, fall out of the bounds of a specific format, or even constrain the allowable values to a predefined set. To help in this task, PostgreSQL offers an array of datatypes that can be assigned to each column in a table. Each datatype forces the data to conform to a predetermined set of rules inherent to that datatype, such as size, type (string, integer, or decimal, for instance), and format (ensuring that it conforms to a valid date or time representation, for example). The behavior of these datatypes can be further tuned through the inclusion of attributes. This section introduces PostgreSQL s supported datatypes, as well as many of the commonly used attributes. Because many datatypes support the same attributes, the definitions are grouped under the heading Datatype Attributes rather than presented for each datatype. Any special behavior will be noted as necessary, however. PostgreSQL also offers the ability to create composite types and domains. A composite type is, in simple terms, a list of base types with associated field names. Domains are also derived from other types, but are based on a particular base type. However, they usually have some type of constraint that limits their values to a subset of what the underlying base type would allow. We will cover both of these features in this section as well. Datatypes Because PostgreSQL enables users to create their own custom types, any discussion of PostgreSQL s datatypes is bound to be incomplete. For purposes of the discussion here, we will cover the most common datatypes, offering information about the name, purpose, format, and range of each. If you would like more information on other datatypes offered by PostgreSQL, such as the inettype used for holding IP information, or the byteatype used for holding binary data, be sure to reference Chapter 8, Data Types, of the PostgreSQL online manual. To facilitate later reference of the material here, this section breaks down the datatypes into four categories: date and time, numeric, string, and Boolean.
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