SQL statements can, intentionally or not, require the mixing of different data types in the same expression. PostgreSQL has extensive facilities for evaluating mixed-type expressions.
In many cases a user does not need to understand the details of the type conversion mechanism. However, implicit conversions done by PostgreSQL can affect the results of a query. When necessary, these results can be tailored by using explicit type conversion.
This chapter introduces the PostgreSQL type conversion mechanisms and conventions. Refer to the relevant sections in 8장 and 9장 for more information on specific data types and allowed functions and operators.