SQL CAST Function

The CAST function in SQL converts data from one data type to another. For example, we can use the CAST function to convert numeric data into character string data.

Syntax

The syntax of the CAST function is as follows:

CAST (expression AS [data type])

where [data type] is a valid data type in the RDBMS you are working with.

Examples

We use the following table for our examples.

Table Student_Score

This table contains the following rows:

Table Student_Score

Example 1

SELECT First_Name, CAST(Score AS Integer) Int_Score FROM Student_Score;

Result:

In Example 1, we use the CAST function to convert the Score column from type FLOAT to INTEGER. When we do this, different RDMBS have different rules on how to handle the numbers after the decimal point. In the above example, the numbers after the decimal point are always truncated.

Example 2

SELECT First_Name, CAST(Score AS char(3)) Char_Score FROM Student_Score;

Result:

In Example 2, we use the CAST function to convert the SCORE column from type FLOAT to CHAR(3). When we do this, we only take the first three characters. So, if there are more than three characters, everything after the first three characters is discarded.