Speed Up Question Editing in LearnDash

If your LearnDash-powered LMS has grown to thousands of users and millions of quiz attempts, you’ve probably noticed something frustrating: editing quiz questions becomes slow-sometimes taking several seconds to load.

This happens because LearnDash performs expensive lookups in the quiz statistics table.
The solution?
A single database index that reduces certain queries from multiple seconds to microseconds.

This guide explains exactly how to:

• Your site has more than hundreds of thousands of quiz statistics rows.
• Editing quiz questions feels slow or laggy.
• You want an easy, safe, impactful optimization.

When you update a quiz question, LearnDash runs this kind of query:

SELECT COUNT(*) 
FROM wp_wp_pro_quiz_statistic 
WHERE question_id = <current_question_id>;

On a table with millions of rows and no index on question_id, MySQL must scan the entire statistics table – which can take seconds.

Adding the index tells MySQL:

“You can jump directly to relevant rows instead of scanning everything.”

The result is a nearly instant lookup.

LearnDash installations can differ:

• Older setups → {prefix}wp_pro_quiz_statistic
• Newer → {prefix}learndash_pro_quiz_statistic

To confirm:
WordPress Dashboard → LearnDash LMS → Settings → Support → Database Tables
Look for a row containing: pro_quiz_statistic

In my setup, the table name is `wp_wp_pro_quiz_statistic`. Similarly, my question table name is `wp_wp_pro_quiz_question`.

Run this query to find your latest question ID: (Replace the table name if yours differs. Use Quiz Question table name.)

SELECT `id`
FROM `wp_wp_pro_quiz_question`
ORDER BY `id` DESC
LIMIT 1;

Suppose it returns:

79587

Run: (Replace the table name and question_id if yours differ.)

EXPLAIN ANALYZE
SELECT COUNT(*)
FROM wp_wp_pro_quiz_statistic
WHERE question_id = 79587;

If it takes more than 0.3 seconds, you will benefit from indexing.

In my case:

❌ 8.251 seconds — far too slow.

• How to measure query timing
• Where in LearnDash code the issue occurs
• How indexing fixes it
• [Optional] core file optimization

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Run the following SQL command:(Replace the table name if yours differs.)

ALTER TABLE wp_wp_pro_quiz_statistic
ADD INDEX idx_question_id (question_id);

This typically completes in under a minute.

Run the benchmark again:(Replace the table name if yours differs.)

EXPLAIN ANALYZE
SELECT COUNT(*)
FROM wp_wp_pro_quiz_statistic
WHERE question_id = 79587;

Query Benchmark	Time Before	Time After
Count by question_id	8.251 seconds	0.00001 seconds

You may modify the core file for further improvement. Only do this if you’re experienced with PHP and confident working with LearnDash internals.

In the file sfwd-lms/includes/lib/wp-pro-quiz/lib/model/WpProQuiz_Model_StatisticMapper.php there is a function isStatisticByQuestionId. The existing query as below

return $this->_wpdb->get_var(
    $this->_wpdb->prepare(
        "SELECT
            COUNT(*)
        FROM
            {$this->_tableStatistic}
        WHERE
            question_id = %d",
        $questionId
    )
);

After modifying, it would look like this

return $this->_wpdb->get_var(
    $this->_wpdb->prepare(
        "SELECT
            1
        FROM
            {$this->_tableStatistic}
        WHERE
            question_id = %d
        LIMIT 1",
        $questionId
    )
);

Two changes in the code,
1. Instead of selecting all columns using *, I am selecting 1. This query is specifically to know if a row exists for the question ID.
2. Added a limit of 1.

If you ever need to remove the index(Replace the table name if yours differs.):

ALTER TABLE wp_wp_pro_quiz_statistic
DROP INDEX idx_question_id;

Large LearnDash sites often suffer from slow admin performance due to missing indexes. Fortunately, the fix is straightforward:

Add an index on question_id in the statistics table.

This transforms multi-second queries into instant lookups and significantly improves the question-editing experience.

If you have questions about your setup, need help applying this fix, or want deeper optimizations, feel free to comment below!