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How to use cast in BigQuery?

How to use cast in BigQuery?

Learn how to harness the power of the CAST function in BigQuery to effortlessly transform and manipulate data.

In this article, we will explore how to effectively use the cast function in BigQuery. Understanding the basics of BigQuery is essential before diving into the intricacies of casting data. We will also discuss the syntax of the cast function and provide a step-by-step guide on how to use it. Additionally, we will cover common errors that may occur and provide tips for optimizing your use of cast in BigQuery.

Understanding the Basics of BigQuery

Before we delve into the specifics of casting data in BigQuery, let's first understand what BigQuery is and why it is important. BigQuery is a fully-managed, serverless data warehouse solution provided by Google Cloud. It allows you to analyze massive datasets quickly and efficiently using SQL-like queries.

BigQuery is designed for handling large, complex datasets and performing high-speed analysis. It can process terabytes or even petabytes of data in seconds, making it ideal for data-intensive projects such as business intelligence, data exploration, and machine learning.

But what makes BigQuery truly powerful is its ability to scale effortlessly. It automatically distributes your data and queries across multiple servers, ensuring fast and reliable performance even when dealing with massive amounts of data. This scalability makes BigQuery a versatile tool that can handle a wide range of analytical workloads, from simple ad-hoc queries to complex data transformations.

What is BigQuery?

BigQuery is not just a data warehouse; it is a complete analytics platform. It offers a wide range of features and integrations that enable you to extract maximum value from your data. For example, BigQuery integrates seamlessly with other Google Cloud services such as Cloud Storage, Cloud Dataflow, and Cloud Machine Learning Engine, allowing you to build end-to-end data pipelines and perform advanced analytics.

Moreover, BigQuery supports a variety of data ingestion methods, including batch loading, streaming, and data transfer services. This flexibility allows you to bring data from various sources into BigQuery, ensuring that you have a holistic view of your data for analysis.

Importance of Data Casting in BigQuery

Data casting plays a crucial role in BigQuery. When working with databases, data is often stored in different formats or data types. Casting allows you to convert data from one type to another, ensuring compatibility and accuracy in your analysis. It enables you to manipulate and transform your data effectively, leading to more meaningful insights.

But data casting in BigQuery goes beyond simple type conversions. BigQuery provides a rich set of casting functions that allow you to perform complex transformations on your data. For example, you can use casting functions to extract specific components from a date or timestamp, convert strings to numbers, or even parse JSON data into structured columns.

By leveraging the power of data casting in BigQuery, you can unlock the full potential of your data. It empowers you to explore new dimensions of analysis, uncover hidden patterns, and make data-driven decisions with confidence.

The Syntax of Cast Function in BigQuery

Let's now take a closer look at the syntax of the cast function in BigQuery. The cast function follows a straightforward structure and provides versatility for converting data types.

Breaking Down the Syntax

The syntax for the cast function in BigQuery is:

CAST(expression AS data_type)


  • expression: The value or column to be casted.
  • data_type: The desired data type to which the expression should be casted.

For example, if you have a column named "age" that contains numerical values stored as strings, you can use the cast function to convert them to integers:


This will ensure that the values in the "age" column are treated as integers, allowing you to perform mathematical operations or comparisons on them.

Data Types Supported by Cast

BigQuery supports a wide range of data types for casting. These include:

  1. STRING: Used for storing textual data.
  2. INTEGER: Used for storing whole numbers.
  3. FLOAT: Used for storing decimal numbers.
  4. BOOLEAN: Used for storing true/false values.
  5. DATE: Used for storing dates in the format 'YYYY-MM-DD'.
  6. TIMESTAMP: Used for storing date and time values.
  7. ARRAY: Used for storing arrays or lists of values.
  8. STRUCT: Used for storing structured data with named fields.

Selecting the appropriate data type for casting is crucial to ensure accurate, efficient analysis. It is important to consider the nature of your data and the operations you plan to perform on it. Choosing the wrong data type may lead to unexpected results or performance issues.

For example, if you have a column named "price" that contains decimal numbers, you would want to cast it as FLOAT to preserve the decimal precision. On the other hand, if you have a column named "is_active" that stores true/false values, you would cast it as BOOLEAN to ensure proper handling of these values.

By understanding the syntax and supported data types of the cast function in BigQuery, you can confidently manipulate and transform your data to meet your analysis needs.

Step-by-Step Guide to Using Cast in BigQuery

Now that we have covered the basics, let's dive into a step-by-step guide on how to effectively use the cast function in BigQuery.

Preparing Your Data for Casting

Prior to casting, it is essential to prepare your data for the conversion process. Ensure that the data types in your source column are compatible with the desired target data type. Cleaning and transforming the data as needed will help avoid errors during the casting process.

For example, let's say you have a column that contains dates in the format "YYYY-MM-DD," but you need to cast them as timestamps. Before applying the cast function, you might need to convert the dates to the appropriate timestamp format, such as "YYYY-MM-DD HH:MM:SS". This step ensures that your data is in the correct format for the casting operation.

Implementing the Cast Function

Once your data is prepared, you can proceed with the implementation of the cast function. Simply specify the expression you want to cast, followed by the desired data type. Remember to use the correct syntax and ensure that the casting aligns with your analysis requirements.

It is important to note that the cast function in BigQuery supports various data types, including integers, floats, timestamps, and strings. Depending on your analysis needs, you can cast a column to a different data type to perform calculations, comparisons, or aggregations.

For instance, if you have a column containing numerical values stored as strings, you can use the cast function to convert them to integers or floats. This conversion enables you to perform mathematical operations on the data, such as summing or averaging the values.

Common Errors When Using Cast in BigQuery

While using the cast function in BigQuery, you may encounter some common errors. Understanding and troubleshooting these errors are vital for successful data casting.

Identifying and Troubleshooting Errors

When an error occurs during casting, BigQuery provides detailed error messages that can help you identify and rectify the issue. Analyzing these messages will enable you to pinpoint the exact problem and take the necessary corrective actions.

For example, let's say you are trying to cast a string column to an integer data type. If the string column contains non-numeric characters, BigQuery will throw an error indicating that the casting failed due to invalid input. In this case, you can use the error message to identify the specific row or rows causing the issue and then clean or modify the data accordingly.

Another common error is when you try to cast a column to a data type that is not compatible with its current values. For instance, if you attempt to cast a string column containing non-integer values to an integer data type, BigQuery will generate an error message indicating the casting failed due to a type mismatch. To resolve this, you need to ensure that the data types are compatible before performing the cast.

Best Practices to Avoid Errors

To minimize errors when using the cast function, follow these best practices:

  • Ensure the data types are compatible before casting.
  • Perform data validation and cleansing prior to casting.
  • Handle null values appropriately as they can lead to errors.
  • Regularly test and validate your casting logic.

By adhering to these practices, you can minimize errors and ensure smooth data casting in BigQuery.

It is also important to note that the cast function in BigQuery supports a wide range of data types, including numeric, string, date, and timestamp types. However, there are certain limitations and considerations to keep in mind. For example, when casting from a string to a numeric type, the string must contain a valid numeric representation. Additionally, when casting to a date or timestamp type, the string must be in a specific format that adheres to the respective data type's requirements.

Furthermore, it is worth mentioning that the cast function can be used not only to convert data types but also to change the precision or scale of numeric values. This can be particularly useful when dealing with decimal numbers and needing to round or truncate the values to a specific number of decimal places.

Optimizing Your Use of Cast in BigQuery

Now that you have a solid understanding of the cast function and how to prevent common errors, let's explore some tips for optimizing your use of cast in BigQuery.

Tips for Efficient Casting

To optimize your casting operations in BigQuery, consider the following tips:

  • Try to avoid unnecessary casts whenever possible. Choose the appropriate data type from the start to minimize conversions.
  • Utilize the EXTRACT function to extract specific components from date or timestamp data and cast them to the desired data type.
  • Take advantage of the ARRAY and STRUCT data types in your queries, casting individual elements as needed.

By implementing these tips, you can further enhance the efficiency and accuracy of your data casting operations in BigQuery.

Advanced Casting Techniques

Lastly, let's explore some advanced casting techniques that can be helpful in specific scenarios. BigQuery offers additional functions such as SAFE_CAST and TRY_CAST to handle casting gracefully, especially when dealing with potential conversion errors. Familiarize yourself with these techniques to enhance your casting capabilities in BigQuery.


In conclusion, understanding how to use the cast function in BigQuery is essential for efficient data analysis and manipulation. By following the step-by-step guide, troubleshooting common errors, and implementing optimization techniques, you can enhance your casting operations and derive meaningful insights from your data. BigQuery's powerful features, combined with effective data casting, enable you to unlock the full potential of your data analysis tasks.

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