


How to Update NULL QuestionIDs in a Database Table Using a Related Table?
Jan 10, 2025 am 06:48 AMDatabase Table Update: Aligning Columns with Referenced Values
Your question pertains to updating a database table where the QuestionID column contains null values. You seek to set these null values equal to the corresponding QuestionID values in a related table, 'Answers', referenced by the AnswerID column.
To achieve this, you can leverage an inner join. The following query demonstrates how:
UPDATE QuestionTrackings q INNER JOIN QuestionAnswers a ON q.AnswerID = a.AnswerID SET q.QuestionID = a.QuestionID WHERE q.QuestionID IS NULL;
The INNER JOIN operation establishes a connection between rows in the QuestionTrackings and QuestionAnswers tables based on matching AnswerID values. This allows us to access the QuestionID value from the QuestionAnswers table for each row in the QuestionTrackings table.
You can add additional conditions to the WHERE clause to further narrow down the rows to be updated. For example, if you only want to update rows where QuestionID is null and AnswerID is less than 500:
UPDATE QuestionTrackings q INNER JOIN QuestionAnswers a ON q.AnswerID = a.AnswerID SET q.QuestionID = a.QuestionID WHERE q.QuestionID IS NULL AND q.AnswerID < 500;
It's recommended to preview the rows to be updated using a select query before executing the update to ensure accuracy:
SELECT * FROM QuestionTrackings q INNER JOIN QuestionAnswers a ON q.AnswerID = a.AnswerID WHERE q.QuestionID IS NULL;
This will help you verify that each AnswerID has only one associated QuestionID and avoid potential errors during the update process.
The above is the detailed content of How to Update NULL QuestionIDs in a Database Table Using a Related Table?. For more information, please follow other related articles on the PHP Chinese website!

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