CAST Function in SQL - sql - sql tutorial - learn sql




 sql cast function
  • In SQL Server (Transact-SQL), the CAST function converts an expression from one datatype to another datatype.
  • 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

Column Name Data Type
StudentID integer
First_Name char(20)
Score float

This table contains the following rows:

Table Student_Score

StudentID First_Name Score
1 Jenny 85.2
2 Bob 92.5
3 Alice 90
4 James 120.1

Example 1

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

Result:

First_Name Int_Score
Jenny 85
Bob 92
Alice 90
James 120
  • 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:

First_Name Char_Score
Jenny 85.
Bob 92.
Alice 90
James 120
  • 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.

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