How to Cast Data Types in Postgres for SELECT Statements?

Casting Data Types in Postgres for SELECT Statements

When working with Postgres, it may be necessary to convert data from one type to another for use in a SELECT statement. One common scenario is casting a varchar column to an integer. While it is possible to perform this operation in Java, Postgres provides native support for data type casting.

To cast a varchar column to an integer, use one of the following syntax options:

• cast(varchar_col AS int): This is the SQL standard syntax.
• varchar_col::int: This is a Postgres-specific shorthand notation.

For example, consider the following query:

<code class="sql">SELECT cast(age AS int) FROM users;</code>

This query would convert the age column, which is of type varchar, to an integer.

Other variations of the syntax include:

• int4(varchar_col): Works only for certain type names.
• int '123': Requires an untyped, quoted string literal.

It's important to ensure that the string value being converted meets the requirements for the target integer type. This includes having an optional leading sign ( /-) followed by digits only. Leading or trailing whitespace is ignored.

Refer to Postgres documentation for further details on data type casting.

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