How to Fill Missing Dates in a MySQL Dataset Using a Numbers Table?

MySQL: Fill missing dates in date range

In the field of data management, it is very common to encounter data sets containing missing dates. To solve this problem, MySQL provides a solution to fill in these missing dates, ensuring a continuous date sequence.

The key to filling in missing dates in MySQL is to utilize the number table trick. This method involves creating a table called "numbers" that contains an auto-incrementing integer column, effectively an incrementing list of numbers.

Next, populate the "numbers" table with enough rows. This ensures a sufficient range of increasing numbers to cover the desired date range.

To build a list of dates, use the DATE_ADD function. Specifically, in the following query, replace "2010-06-06" and "2010-06-14" with your own start and end dates (make sure to use YYYY-MM-DD format):

<code class="language-sql">SELECT DATE_ADD('2010-06-06', INTERVAL `n`.`id` - 1 DAY)
FROM `numbers` `n`
WHERE DATE_ADD('2010-06-06', INTERVAL `n`.`id` -1 DAY) < '2010-06-14';</code>

Use the results of this query as an intermediate table to perform a LEFT JOIN on the original data table based on the time part:

<code class="language-sql">SELECT `x`.`ts` AS `timestamp`,
       COALESCE(`y`.`score`, 0) AS `cnt`
FROM (SELECT DATE_FORMAT(DATE_ADD('2010-06-06', INTERVAL `n`.`id` - 1 DAY), '%m/%d/%Y') AS `ts`
      FROM `numbers` `n`
      WHERE DATE_ADD('2010-06-06', INTERVAL `n`.`id` - 1 DAY) < '2010-06-14') `x`
LEFT JOIN `your_table` `y` ON DATE(`y`.`date_column`) = DATE(`x`.`ts`);</code>

To maintain the date format, wrap the above ts field in a DATE_FORMAT function:

<code class="language-sql">DATE_FORMAT(`x`.`ts`, '%d.%m.%Y') AS `timestamp`</code>

By following these steps, you can efficiently fill in missing dates in your MySQL dataset, ensuring a seamless representation of the required date range.

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