How To Guides
How to use cast in in BigQuery?

How to use cast in in BigQuery?

Learn how to harness the power of the CAST function in BigQuery with our comprehensive guide.

BigQuery is a powerful tool that allows you to analyze massive datasets quickly. One essential aspect of working with data in BigQuery is understanding how to use the CAST function. In this article, we will explore the basics of BigQuery, dive into the definition and role of the CAST function, discuss its syntax and usage, provide a step-by-step guide on using CAST in BigQuery, and troubleshoot common errors that may occur along the way.

Understanding the Basics of BigQuery

Before we delve into the details of using the CAST function, let's first gain a clear understanding of what BigQuery is. BigQuery is a fully-managed data warehouse solution provided by Google Cloud Platform (GCP). It allows you to perform ad-hoc queries on large-scale datasets using SQL-like syntax, making it easy to analyze and draw insights from your data.

BigQuery operates on a distributed architecture, leveraging the power of Google's infrastructure to process and analyze data at incredible speeds. It is designed to handle a massive amount of data, making it an ideal solution for organizations dealing with large datasets.

What is BigQuery?

BigQuery is a cloud-based, serverless, and highly scalable data warehouse that allows you to analyze your data using SQL-like syntax. It handles all the infrastructure management for you, allowing you to focus on extracting valuable insights from your data. With BigQuery, you can run SQL queries on massive datasets within seconds or minutes, eliminating the need for traditional data warehouses that require extensive hardware and resource provisioning.

Importance of Data Type Conversion in BigQuery

When working with data in BigQuery, it is crucial to understand the importance of data type conversion. BigQuery has strict typing rules, meaning that operations between incompatible data types can result in errors. The CAST function provides a solution by allowing you to convert data from one type to another, enabling seamless data manipulation and analysis.

By utilizing the CAST function, you can transform your data into the desired data type for further analysis or comparison purposes. Whether it's converting a string to a numeric value or changing the format of a date, the CAST function plays a crucial role in ensuring data integrity and accuracy in your BigQuery projects.

Furthermore, data type conversion is not only important for data manipulation but also for optimizing query performance. By converting data to the appropriate type, you can take advantage of BigQuery's query optimization techniques, such as using appropriate indexes and compression algorithms, to speed up query execution and reduce costs.

Additionally, understanding data type conversion in BigQuery allows you to handle data from different sources seamlessly. When integrating data from various systems or importing data from external sources, you may encounter data with different formats or types. The ability to convert and standardize the data using the CAST function ensures consistency and compatibility throughout your analysis.

Introduction to CAST Function in BigQuery

Now that we have a solid understanding of BigQuery and the significance of data type conversion, let's delve into the CAST function itself.

Definition of CAST Function

The CAST function in BigQuery is used to convert data from one data type to another. It allows you to specify the target data type explicitly, ensuring that the resulting value aligns with your desired format or compatibility requirements. The CAST function follows the SQL standard, making it familiar to those experienced with SQL databases.

The Role of CAST Function in BigQuery

The CAST function plays a significant role in data manipulation and analysis in BigQuery. It enables you to perform operations that involve incompatible data types, such as arithmetic calculations or comparisons. By converting data to the appropriate type using the CAST function, you can ensure accurate and meaningful results for your data analysis tasks.

One of the key advantages of the CAST function is its ability to handle various data types seamlessly. For example, let's say you have a column in your BigQuery table that stores dates as strings. To perform date-based calculations or comparisons, you would need to convert these strings into the date data type. This is where the CAST function comes in handy. By applying the CAST function to the date column, you can effortlessly convert the strings into the desired date format, allowing you to perform complex date operations with ease.

Furthermore, the CAST function in BigQuery supports a wide range of data types, including numeric, string, date, time, and timestamp. This versatility enables you to convert data between different formats, ensuring compatibility across various analytical tasks. Whether you need to convert a string to a numeric value for mathematical calculations or transform a timestamp into a date for time-based analysis, the CAST function provides the flexibility to handle diverse data types efficiently.

Syntax and Usage of CAST Function

Now that we understand the definition and role of the CAST function, let's take a closer look at its syntax and explore its various usage scenarios in BigQuery.

Breaking Down the Syntax of CAST Function

The CAST function in BigQuery follows a straightforward syntax:

  1. Start by specifying the value you want to convert.
  2. Follow it with the keyword 'CAST'.
  3. Within parentheses, place the value you want to convert and specify the target data type using the keyword 'AS'.
  4. Finally, close the parentheses to complete the CAST function.

For example, consider the following query:

SELECT CAST('42' AS INT64) AS converted_value;

In this query, the CAST function is used to convert the string '42' to an INT64 data type, resulting in the converted value of 42.

Common Use Cases of CAST Function

The CAST function is a versatile tool that can be used in various scenarios within BigQuery. Some of the common use cases include:

  • Converting strings to numeric values, such as casting a string representation of a number to an INT64 or FLOAT64 data type.
  • Changing the format of date or timestamp values, allowing you to perform date arithmetic or extract specific components.
  • Converting between different timestamp formats or time zones for consistency and comparison purposes.
  • Transforming arrays or structs into other data types for further analysis or manipulation.

The flexibility and power of the CAST function make it an essential tool in your BigQuery toolbox, enabling you to handle a wide range of data transformation scenarios with ease.

Step-by-Step Guide to Using CAST in BigQuery

Now that we have covered the basics, let's walk through a step-by-step guide on using the CAST function in BigQuery.

Preparing Your BigQuery Environment

Before you can begin using the CAST function in BigQuery, you need to ensure that you have a properly configured environment. This involves setting up a project in Google Cloud Platform, enabling BigQuery, and creating a dataset to work with. Once you have your environment set up, you're ready to proceed.

Executing a CAST Function

To execute a CAST function in BigQuery, follow these steps:

  1. Start by opening the BigQuery web UI or utilizing the command-line tool, depending on your preferred method of interaction.
  2. Select the project and dataset that contain the data on which you want to perform the CAST function.
  3. Construct and execute a query that includes the CAST function, specifying the value you want to convert and the target data type.
  4. Review the output of the query and validate that the CAST function produced the expected results.

By following these steps, you can seamlessly execute the CAST function within BigQuery and leverage its power to manipulate and analyze your data with precision.

Troubleshooting Common Errors with CAST in BigQuery

Despite the simplicity of using the CAST function, you may encounter some errors along the way. Here, we will discuss common error messages and provide tips for avoiding and resolving them.

Understanding Error Messages

When working with the CAST function, BigQuery can generate error messages that provide insight into the cause of the issue. These error messages may indicate mismatches between the value and the target data type or other compatibility issues.

By carefully reviewing the error messages, you can pinpoint the problem and take the necessary steps to fix it. Understanding the error messages is crucial in resolving any issues that arise during the usage of the CAST function.

Tips for Avoiding and Resolving Errors

To avoid errors and ensure smooth execution of the CAST function, consider these tips:

  • Verify that the value you are converting matches the target data type's format and requirements.
  • Double-check the syntax of the CAST function, ensuring that proper parentheses and keywords are used.
  • Take advantage of BigQuery's schema inference capabilities to determine the data types of your columns and avoid unnecessary conversions.
  • Use data preview and sample queries to validate the results before executing complex queries involving the CAST function.
  • Refer to the BigQuery documentation and community resources for further guidance on specific error messages and troubleshooting steps.

By adopting these best practices, you can minimize the occurrence of errors and troubleshoot any issues efficiently, ensuring a smooth experience when using the CAST function in BigQuery.


In conclusion, understanding how to use the CAST function in BigQuery is essential for manipulating, analyzing, and deriving meaningful insights from your data. By grasping the fundamentals of BigQuery, appreciating the significance of data type conversion, and mastering the syntax and usage of the CAST function, you can confidently handle a wide variety of data transformation tasks within BigQuery.

Remember to follow the step-by-step guide for using the CAST function, troubleshoot any encountered errors skillfully, and always refer to the BigQuery documentation when in doubt. With these skills in your repertoire, you are well-equipped to harness the power of BigQuery and unlock the full potential of your data analysis endeavors. Happy querying!

New Release

Get in Touch to Learn More

See Why Users Love CastorDoc
Fantastic tool for data discovery and documentation

“[I like] The easy to use interface and the speed of finding the relevant assets that you're looking for in your database. I also really enjoy the score given to each table, [which] lets you prioritize the results of your queries by how often certain data is used.” - Michal P., Head of Data