How to Cast Data Types in Postgres SELECT Statements?

Casting Data Types in Postgres SELECT Statements

In Postgres SQL, casting a value from one data type to another is essential for database operations. When a column's data type is inconsistent with the desired outcome, it becomes necessary to perform a data type cast.

Performing Data Type Casting

To cast a data type in a SELECT statement, simply utilize the CAST keyword or the Postgres syntax shorthand ::, followed by the desired data type enclosed in parentheses. For converting a varchar column to int, the following syntax would suffice:

<code class="sql">CAST(varchar_col AS int)</code>

<code class="sql">varchar_col::int</code>

Additional Considerations

• The CAST keyword is the preferred method as it adheres to the SQL standard.
• The :: shorthand may require additional parentheses in certain syntax scenarios.
• Alternative casting methods include using the internal type name (e.g., int4(varchar_col)) or casting an untyped string literal (int '123').
• Casting to int requires a string consisting of an optional sign ( /-) followed exclusively by digits, ignoring leading/trailing whitespace.
• Details on data type casting can be found in the Postgres documentation here and here.

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