MATCH AGAINST sql with keyword ‘with’

Introduction

In this article, we’ll explore how to use the MATCH AGAINST function in MySQL to search for specific keywords within a column of text data. We’ll also delve into the specifics of why certain words may not be matching as expected.

Understanding MATCH AGAINST

The MATCH AGAINST function is used to measure the similarity between a set of words (in this case, the keyword we’re searching for) and a collection of words contained within a column of text data. This function returns a value that represents how well the search keywords match the content in the specified column.

When you use MATCH AGAINST, MySQL performs several steps:

1. Tokenization: The text is broken down into individual words (tokens).
2. Stopword removal: Common words like “the,” “and,” etc., are removed from the tokenized list.
3. Stemming or Lemmatization: Words are reduced to their base form (e.g., “running” becomes “run”).
4. Matching: The search keywords are compared against the processed tokens.

Why Doesn’t ‘with’ Match?

In the provided example, we’re searching for a keyword called “their_very_nice_last_name”. However, when trying to find data containing the word “with”, MySQL returns no results. To understand why this might be happening, let’s examine what happens during the tokenization and stopwords removal steps.

When we use MATCH AGAINST with ‘with’, here’s how it works:

• The text is tokenized into words.
• Stopwords are removed from the list of tokens (which includes “with”).
• Since “with” has been removed, the search for ‘with’ will not match any data containing this word.

Solving the Issue

To resolve this issue, we need to adjust our MySQL configuration by removing the stopwords that contain the keyword ‘with’. In other words, we want MySQL to stop removing ‘with’ from the tokenized list of words.

Here’s how you can do it:

• Locate your MySQL configuration file (my.cnf or my.ini, depending on your operating system).

• Update the following parameter: ft_stopword_file.

  [mysqld]
  ...
  # Specify a new location for stopwords
  ft_stopword_file = /path/to/your/stopwords.txt
  

`

In this example, we’re telling MySQL to use a custom file /path/to/your/stopwords.txt that lists the words you want to keep during tokenization. If you don’t have such a file, create one and list all your stopwords in it.

Additionally, when updating ft_stopword_file, consider running the following command:

mysql -u root -e "REBUILD INDEXES FOR KEY 'family.search_keywords'"

This rebuilds indexes on the column containing the search keywords. You can also use this method to speed up your searches, but it depends on the size and complexity of your data.

Conclusion

In summary, when using MATCH AGAINST with a specific keyword and encountering issues like “with” not matching, you may need to adjust your MySQL configuration by specifying custom stopwords in your ft_stopword_file. This ensures that the specified keywords are preserved during tokenization and stopwords removal. Remember to rebuild indexes after making these changes.

Best Practices

Here are some best practices for using MATCH AGAINST with caution:

• Always review your MySQL configuration file (my.cnf or my.ini) before applying changes.
• Consider using a custom stopwords file to avoid removing keywords during tokenization.
• Update your stopwords regularly to reflect changes in your data.

Limitations of MATCH AGAINST

While MATCH AGAINST is an effective function for searching text columns, there are some limitations you should be aware of:

• Matching sensitivity: The match score depends on the similarity between the search keywords and the content in the column. Be cautious when applying filters or sorting results based on this score.
• Performance overhead: MATCH AGAINST can impact performance, especially for large columns with many words. Consider optimizing your query or indexing strategy if you notice decreased performance.

Real-World Applications

MATCH AGAINST has a wide range of real-world applications:

• Search functionality: Use MATCH AGAINST to build search bars for web applications.
• Content filtering: Employ MATCH AGAINST in filters and search bars within databases.
• Recommendation systems: Match user preferences against available products or services.

Common Variations

Here are some common variations of the MATCH AGAINST function:

MATCH (field, keyword)

Matches a specific word in the field column.

SELECT * 
FROM table_name 
WHERE MATCH (column_to_search) AGAINST ('search_keyword')

MATCH (field, keyword, mode = 'any')

Allows searching for multiple keywords with an “or” condition.

Last modified on 2023-11-10