Filtering Words Using Regular Expression in BigQuery Table

In this article, we will explore how to filter words using regular expression in a BigQuery table. We will delve into the world of SQL queries and BigQuery’s regular expression functionality to extract specific values from a column.

Introduction to BigQuery Regular Expressions

BigQuery provides support for regular expressions through the REGEXP_CONTAINS and REGEXP_EXTRACT functions. These functions allow you to perform text matching and pattern extraction on a string column.

REGEXP_CONTAINS Function

The REGEXP_CONTAINS function checks if a string contains a specified regular expression pattern. It returns TRUE if the string matches the pattern, and FALSE otherwise.

REGEXP_EXTRACT Function

The REGEXP_EXTRACT function extracts a substring from a string based on a specified regular expression pattern. It returns the matched substring or an empty string if no match is found.

Understanding the Problem

In your question, you are trying to filter words in a column called [manfacturing_output] that contain only quotes (") and extract the text within the quotes. However, you’re getting errors with SQL queries.

Solution: Using REGEXP_CONTAINS and REGEXP_EXTRACT Functions

We will use the REGEXP_CONTAINS function to filter words that do not contain only quotes, and then use the REGEXP_EXTRACT function to extract the text within the quotes.

Here’s an example query:

WITH data AS (
  SELECT
    "The category is \"Clamp Break\"." AS manfacturing_output
  UNION ALL
  SELECT
    "Turner Usability" AS manfacturing_output
  UNION ALL
  SELECT
    "The category for the response is \"Clamp Break\"." AS manfacturing_output
  UNION ALL
  SELECT
    "The category for this response is \"Turner Usability\"." AS manfacturing_output
  UNION ALL
  SELECT
    "Clamp Break" AS manfacturing_output
  UNION ALL
  SELECT
    "The category is \"Machine &amp; Errors\"." AS manfacturing_output
  UNION ALL
  SELECT
    "The category for the response is \"Turner Usability\"." AS manfacturing_output )
SELECT
  manfacturing_output,
  CASE
    WHEN REGEXP_CONTAINS(manfacturing_output, r'\\"') THEN REGEXP_EXTRACT(manfacturing_output, r'\"(.*?)\"')
  ELSE
    manfacturing_output
END
  AS output
FROM
  data

In this query, we first use REGEXP_CONTAINS to check if the string contains a double quote (") followed by another double quote (") and then any characters (represented by .*?). If the string matches this pattern, it means that only one quote is present.

If the string does not match this pattern, we fall back to using manfacturing_output as is.

Next, we use REGEXP_EXTRACT to extract the text within the quotes. The regular expression r'\"(.*?)\"' matches a double quote followed by any characters (captured in group 1) and then another double quote.

Example Use Case

Suppose you have a table called my_table with a column called [manfacturing_output]. You want to extract the text within the quotes for each row.

WITH data AS (
  SELECT
    "The category is \"Clamp Break\"." AS manfacturing_output
  UNION ALL
  SELECT
    "Turner Usability" AS manfacturing_output
  UNION ALL
  SELECT
    "The category for the response is \"Clamp Break\"." AS manfacturing_output
  UNION ALL
  SELECT
    "The category for this response is \"Turner Usability\"." AS manfacturing_output
  UNION ALL
  SELECT
    "Clamp Break" AS manfacturing_output
  UNION ALL
  SELECT
    "The category is \"Machine &amp; Errors\"." AS manfacturing_output
  UNION ALL
  SELECT
    "The category for the response is \"Turner Usability\"." AS manfacturing_output )
SELECT
  manfacturing_output,
  CASE
    WHEN REGEXP_CONTAINS(manfacturing_output, r'\\"') THEN REGEXP_EXTRACT(manfacturing_output, r'\"(.*?)\"')
  ELSE
    manfacturing_output
END
  AS output
FROM
  my_table

This query will return the text within the quotes for each row.

Conclusion

In this article, we have explored how to filter words using regular expression in a BigQuery table. We have discussed the REGEXP_CONTAINS and REGEXP_EXTRACT functions and provided an example use case. With these functions, you can extract specific values from a column and perform text matching on your data.

Additional Tips

Always test your queries with sample data to ensure they produce the desired results.
Use the BigQuery documentation to learn more about regular expressions and how to use them in your queries.
Consider using the REGEXP_REPLACE function to replace text patterns in your column.

Common Regular Expression Patterns

Here are some common regular expression patterns that you may encounter:

\\": Matches a double quote (")
[^\\\"]: Matches any character except a double quote (") or a backslash (\)
.*?: Matches any characters (except newline) in a non-greedy manner

These patterns can be used to extract text within quotes, remove whitespace, and more.

Debugging Regular Expression Queries

If you encounter errors with your regular expression query, try the following:

Check the regular expression pattern for syntax errors.
Test the regular expression pattern with a simple string to ensure it produces the desired result.
Use the REGEXP_EXPLAIN function to get an explanation of how the regular expression engine is interpreting your pattern.

By following these tips and understanding regular expressions, you can write efficient and effective queries in BigQuery.

Last modified on 2023-08-18