MS SQL Server - Type Conversion

When we process data in MS SQL Server, we often need to perform calculations or filter results based on data type. Correctly converting data types ensures that our calculations are accurate and queries return the required results. In this article, we will discuss various type conversions in MS SQL Server.

Built-in data types in MS SQL Server

MS SQL Server has various built-in data types to store different types of data. These are common built-in data types in MS SQL Server -

• int: used to store integers.

• decimal: Data type used to store decimal numbers.

• varchar: used to store variable-length strings.

• dateTime: used to store date and time values.

• bit: used to store Boolean values.

Example

Consider a table called "Products". It contains information about the product, name, price and stock quantity. We can define the "price" column as decimal data type and the "quantity_in_stock" column as int data type.

Implicit data type conversion

MS SQL Server will automatically convert one data type to another data type if necessary when performing operations on different data types. This is called implicit data type conversion.

Example

Consider a table named "sales". It contains information about sales, sales prices and sales quantities. Write a query to calculate total sales revenue as shown below −

SELECT sale_price * quantity_sold AS total_revenue FROM sales

In this query, MS SQL Server will automatically convert the value of quantity_sold from the int data type to the decimal data type. Then do the multiplication. Since we cannot multiply int and decimal without converting one of the values ​​first.

Explicit data type conversion

We can also use the CAST and CONVERT functions to explicitly convert data types.

• CAST functionConverts an expression of one data type to another data type. The syntax of the CAST function is as follows:

CAST ( expression AS data_type [ ( length ) ] )

• CONVERT functionConverts an expression of one data type to another data type with a specific formatting style. The syntax of the CONVERT function is as follows:

CONVERT ( data_type [ ( length ) ] , expression [ , style ] )

Example

Consider a table named "orders". It contains information about the order, including the order date. Write a query to retrieve the order date as a string in "MM/DD/YYYY" format as shown below -

SELECT CONVERT(varchar, order_date, 101) AS 'Order Date' FROM orders

In this query, we use the CONVERT function to convert the order_date value to the varchar data type with format style 101. It represents the format "MM/DD/YYYY".

Convert data types in queries

We can also use data type conversion in queries to convert data types to different data types. This is particularly useful when filtering query results.

Example

Consider the "products" table from the previous example. You want to filter the results to only show products with a price below 10. The query will look like this

SELECT *
FROM products
WHERE CAST(price AS int) < 10

In this query, we use the CAST function to convert the price value to the int data type. This way we can compare it to the integer value 10.

Handling conversion errors

Sometimes, conversion errors may occur when converting data types. For example, if we try to convert a string value to an integer, and the string is not a valid integer value. Therefore, MS SQL Server throws a conversion error. To handle these errors, we can use the TRY_CONVERT function. It attempts to convert a value to the specified data type. If the conversion fails, NULL is returned.

Example

Consider a table named "employees". It contains information about the employee, employee ID, and hire date. You want to filter the results to show only employees hired before a specific date. But hire date is stored as varchar data type. We can write a query like this -

SELECT *
FROM employees
WHERE TRY_CONVERT(date, hire_date) < '01/01/2022'

In this query, we use the TRY_CONVERT function. It attempts to convert the value of hire_date to date data type. If the conversion fails, the function returns NULL. It prevents the query from throwing conversion errors.

in conclusion

MS SQL Server has built-in data types and functions for performing type conversions. You should know that converting data types correctly is essential to writing accurate and efficient queries. By using the techniques discussed in this article, you can ensure that your queries return the results you need, even when working with different types of data.

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