Chapter 12. Extending SQL: Functions
- Table of Contents
- 12.1. Introduction
- 12.2. Query Language (SQL) Functions
- 12.2.1. Examples
- 12.2.2. SQL Functions on Base Types
- 12.2.3. SQL Functions on Composite Types
- 12.2.4. SQL Functions Returning Sets
- 12.3. Procedural Language Functions
- 12.4. Internal Functions
- 12.5. C Language Functions
- 12.5.1. Dynamic Loading
- 12.5.2. Base Types in C-Language Functions
- 12.5.3. Version-0 Calling Conventions for C-Language Functions
- 12.5.4. Version-1 Calling Conventions for C-Language Functions
- 12.5.5. Composite Types in C-Language Functions
- 12.5.6. Writing Code
- 12.5.7. Compiling and Linking Dynamically-Loaded Functions
- 12.6. Function Overloading
- 12.7. Procedural Language Handlers
12.1. Introduction
As it turns out, part of defining a new type is the definition of functions that describe its behavior. Consequently, while it is possible to define a new function without defining a new type, the reverse is not true. We therefore describe how to add new functions to PostgreSQL before describing how to add new types.
PostgreSQL provides four kinds of functions:
query language functions (functions written in SQL)
procedural language functions (functions written in, for example, PL/Tcl or PL/pgSQL)
internal functions
C language functions
Every kind of function can take a base type, a composite type, or some combination as arguments (parameters). In addition, every kind of function can return a base type or a composite type. It's easiest to define SQL functions, so we'll start with those. Examples in this section can also be found in funcs.sql and funcs.c in the tutorial directory.
Throughout this chapter, it can be useful to look at the reference page of the CREATE FUNCTION command to understand the examples better.
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