conversion

CAST()

Converts a value from one data type to another, such as a number to text or text to a number.

Description

CAST converts a value from one data type into another. Common uses include turning a number into text so it can be concatenated with other strings, turning text into a number so it can be used in math, or turning text into a proper date.

Syntax

CAST(expression AS type)

Parameters

Name	Description	Optional
expression	The value or column being converted.	No
type	The data type to convert into, for example `VARCHAR`, `INTEGER`, `DOUBLE`, or `DATE`.	No

Return Type

CAST returns a value of whatever type is specified after AS. The "return type" is determined entirely by the target type you choose.

Examples

Store (Customers/Orders/Products)

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Store (Customers/Orders/Products)

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CAST is essential before concatenating numbers

Some databases automatically convert numbers to text when you use CONCAT or ||, but others don't. Explicitly using CAST(price AS VARCHAR) makes your query work reliably across different database engines.

Common Mistakes

Casting text that isn't actually a valid number or date. CAST('abc' AS INTEGER) fails because 'abc' can't be interpreted as a number.
Forgetting that CAST can lose precision. Casting a DOUBLE like 19.99 to INTEGER truncates it to 19, which may not be the rounding behavior you wanted; use ROUND first if you need to round rather than truncate.
Casting when it isn't needed. Many databases implicitly convert compatible types (like comparing an integer column to a numeric literal), so an explicit CAST is only required when types genuinely don't match.