Structured Query Language (SQL) is a programming language used to manage and manipulate relational databases. The SQL Server is one of the most popular relational database management systems used today.

SQL Server is robust, and it supports many functions, including the CAST() function. The CAST() function converts a data type to a different data type explicitly.

This article will cover the basics of SQL Server CAST() function, including how to use it and examples of when to use it.

## Implicit and Explicit Conversions

Before we dive into the syntax and examples of using the CAST() function, it’s essential to understand implicit and explicit conversions. Implicit conversions occur automatically when SQL Server performs a conversion from one data type to another.

Explicit conversions, on the other hand, require a CAST() function to explicitly convert a data type to another data type.

## Syntax of the CAST() Function

The CAST() function syntax consists of two parameters: an expression and a data type to convert the expression to. The expression can be a column, variable, or any valid SQL expression.

The data type parameter can be any valid SQL Server data type, such as INT, CHAR. Here is an example of the syntax:

## SELECT CAST(expression AS data_type)

The CAST() function is a powerful tool that can convert data from one type to another. Let us look at some examples to illustrate this point.

## Examples of Using the CAST() Function

Example 1: Converting Decimal to Integer

Suppose we had a table of sales items, including the total cost of each item. The total cost is a decimal value, but we want to show it as an integer.

We can use the CAST() function to convert the decimal value to an integer. Here is the syntax:

SELECT CAST(total_cost AS INT) FROM Sales.Orders;

Example 2: Converting Decimal to Another Decimal with Different Length

Suppose we had another table of item details that contains the price of each item.

The price is a decimal value with a length of six decimal places. We want to convert it to a decimal value with only three decimal places.

## Here is the syntax:

SELECT CAST(price AS DECIMAL(10,3)) FROM Sales.Order_Items;

Example 3: Converting String to a Datetime Value

Suppose we had a table of clients that includes the date of each client’s birth. The date is stored as a string value, and we want to convert it to a datetime value.

## Here is the syntax:

SELECT CAST(birth_date AS DATETIME) FROM Clients;

Example 4: Using CAST() Function with Arithmetic Operators

Suppose we had a table of sales items and the total cost and discount of each item. The total cost and discount are decimal values.

We want to calculate the discounted price, which is the total cost minus the discount. We can use the CAST() function to convert the decimal values to integer values and perform arithmetic operations.

## Here is the syntax:

SELECT CAST(total_cost AS INT) – CAST(discount AS INT) AS discounted_price FROM Sales.Orders;

## Conclusion

In conclusion, the CAST() function is a powerful tool in SQL Server. It allows us to convert data types explicitly and perform arithmetic operations on the converted values.

Understanding how to use the CAST() function is essential for writing complex SQL queries that manage and manipulate relational databases. In summary, the SQL Server CAST() function is a powerful tool for managing and manipulating relational databases.

Using explicit conversions with the CAST() function is important for writing complex SQL queries that require conversions between data types. Implicit and explicit conversions, syntax, and examples are some of the points covered in this article.

The takeaway from this discussion is that the CAST() function is a powerful tool for data manipulation. Understanding its proper use is a necessary skill for SQL developers, database administrators, and data analysts.