PostgreSQL 7.2.1 Documentation
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# Chapter 5. Type Conversion

# 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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