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Chapter 5. Type Conversion

Table of Contents
5.1. Introduction
5.2. Overview
5.3. Operators
5.4. Functions
5.5. Query Targets
5.6. UNION and CASE Constructs

5.1. Introduction

SQL queries can, intentionally or not, require mixing of different data types in the same expression. PostgreSQL has extensive facilities for evaluating mixed-type expressions.

In many cases a user will not need to understand the details of the type conversion mechanism. However, the implicit conversions done by PostgreSQL can affect the results of a query. When necessary, these results can be tailored by a user or programmer using explicit type coercion.

This chapter introduces the PostgreSQL type conversion mechanisms and conventions. Refer to the relevant sections in Chapter 3 and Chapter 4 for more information on specific data types and allowed functions and operators.

The Programmer's Guide has more details on the exact algorithms used for implicit type conversion and coercion.

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