What Are the Steps to Cast INT in SQL for Type Conversion?

Data type conversion is one of the essential tasks in data management and analysis. In this article, we’ll take a closer look at a very distinct conversion type – converting INT data type to other data types and vice versa.

We’ll explore some typical situations and pitfalls you can encounter when converting INT. There will also be several interview question examples to showcase how this conversion works.

What is Casting INT in SQL?

Casting or converting data types in SQL means changing a value from one data type to another.

Specifically, casting INT means converting the integer data type to another data type – typically a numerical one – and vice versa.

The standard SQL function for conversion supported in all databases is CAST() or? CAST AS SQL Function . Another function that does the same job is CONVERT(), but it’s SQL Server-specific.

Situations Where Casting INT is Necessary in SQL

In general, there are four typical situations where casting to or from INT will be necessary.

1. Data Calculations

It’s very common that performing data calculations involves mathematical operations on two or more different numerical data types.

For example, the number of rides is stored as DECIMAL, the same as the number of passengers. If you want to calculate the average number of passengers by ride for each driver, you’d divide the number of passengers by the number of rides.

However, you should cast the values to DECIMAL before that, as you want to show this ratio as a decimal number. Otherwise, you’d end up with incorrect results, as multiplying an integer with a decimal results in an integer. In other words, you’d lose decimal points.

2. Data Standardization

Another example is when you want to ensure data types are consistent and logical, considering the data they should represent.

For instance, order IDs are often stored as INT. Usually, the discount rate would be stored as a numerical type. But it can also happen that it’s VARCHAR.

With this data being VARCHAR, you can’t do any mathematical operations, e.g., calculating the discount amount by multiplying the amount with the discount rate. So, it’s recommended to cast the discount rate to INT and make data ready for further calculations.

3. Transferring Data Between Systems

Different systems can use different data types for the same data. If you have to move data from one system to another, the data types have to match the goal system data type requirements. So, you’ll have to convert all integers to, say, FLOAT. Otherwise, you risk incompatibility, data loss, and corruption.

4. Error Prevention

Error, in this case, means type mismatch when incompatible types are used in operations or functions.

For example, you might want to concatenate the order ID with the hyphen and customer name to get, e.g., 1-Art Vandeley.

Sure, you can use CONCAT(). However, this won’t work because the order ID is an integer. So, you first need to convert it to VARCHAR, as CONCAT() works only with textual data. Only then can you proceed with concatenation.

Overview of the Steps Involved in Casting INT in SQL

Casting is not complicated and consists of four relatively simple steps. However, the most important is the first one; the other three steps are just technicalities.

1. Identify the Need for Casting: The most important step is to recognize the need for casting INT in SQL. If you don’t, your query won’t run or, even worse, it will return incorrect results.

2. Choose the Function for Casting: This step applies only to SQL Server users; they can choose between CAST() and CONVERT(). Users of other databases will have no choice but to use CAST().

3. Write the Query: In this step, you write the query that implements the casting function to cast to or from INT.

4. Check the Output: Don’t just accept the query output. Check if the conversion yielded the expected result and without errors.

Understanding Data Types in SQL

When casting INT in SQL, it’s important to know the characteristics and the use of the most common data types. Knowing that is crucial to determine, first, if the data conversion is necessary and, second, if the chosen data type fits the kind of data you want to show.

Here’s an overview of the most common data types.

When I talk about choosing the right data type for the data, this involves considering several things.

1. Size and Range: The data type must be able to store the required range of values. For example, don’t use CHAR, which has a maximum of 255 characters, if it’s highly likely your data will go beyond that. Use VARCHAR, which can go up to 65,535 characters.

2. Storage: You should also think about the storage space. In other words, if you know INT will suffice for sure, then don’t use BIGINT just because you can.

3. Precision: Considering precision is important when casting INT to another numerical type. Yes, you want decimals, but how precise should the values be? If you want exact values with the controlled number of decimal places to avoid rounding errors, then use DECIMAL. If you’re fine with approximate values, use FLOAT.

The Syntax for Casting INT in SQL

The CAST() syntax is as follows.

CAST(expression AS data_type)        

The expression is data written in single quotes ('') or, more often, a column name you want to cast. After the keyword AS, you define the output data type.

In PostgreSQL, you can use a shorthand for CAST(), which is a double colon (::).

expression :: data_type        

The SQL Server users might also want to use CONVERT(). It has a very similar, the-other-way-round syntax.

CONVERT(data_type, expression, [style])        

So, here, you first define a data type and then refer to the data you’re converting. All the arguments are separated by a comma. CONVERT() also has the optional style parameter. It defines the format for the conversion. This is mainly used when converting date/time data types to and from string data types, so you won’t be needing this when converting INT.

For more details on comparison of CAST() and CONVERT() for type conversion, handling NULL values and best practices, https://www.stratascratch.com/blog/what-are-the-steps-to-cast-int-in-sql-for-type-conversion/ .