SQL - Retrieve information for a specified time frame using a predetermined value

Question

SQL - Retrieve information for a specified time frame using a predetermined value

I am looking to retrieve data from a table, extract the information using JavaScript, and visualize it on a graph where the x-axis represents dates and the y-axis represents numbers.

The DATA table is structured as follows (please note that attempts to format it as an HTML table using markdown have been unsuccessful):

| date    | number |
|---------|--------|
| 2015-01 | 12     |
| 2015-02 | 7      |
| 2015-04 | 4      |

The SQL query used is:

SELECT date_format(date, '%Y-%m') AS date, number
FROM DATA
WHERE date >= '2015-01' AND date <= '2015-05'
GROUP BY date
ORDER BY date;

While this query returns the same table, I am seeking a solution where each month is represented with a value of 0 if data is not available. For example, if there is no record for March, the desired output would be:

| date    | number |
|---------|--------|
| 2015-01 | 12     |
| 2015-02 | 7      |
| 2015-03 | 0      |
| 2015-04 | 4      |
| 2015-05 | 0      |

The query should cover all months between January and May. However, the start and end dates are variable, spanning multiple years. Is there a SQL solution to this issue, or would post-processing in JavaScript be necessary to achieve this?

Thank you for any assistance provided.

Edit: The date range can vary and encompass multiple years. Considering this, is there a way to handle gap filling directly in SQL, or is post-processing the only viable option?

Edit2: As mentioned by @mauro, the challenge is "gap filling." Given the complexity of solving this in MySQL, I have opted to post-process the results.

For more insights, refer to: How to fill date gaps in MySQL?

javascript mysql sql date select

Answer 1

Answer №1

To improve efficiency, I suggest creating a second table named DATA2 that includes a single row for each month with the number equal to zero. Instead of querying data from the table DATA alone, you can achieve the desired results by querying from a combined dataset:

FROM (SELECT * FROM DATA 
UNION ALL 
SELECT * FROM DATA2) D

By following this approach, you can ensure that even when there are no values for a specific month in DATA, you will still obtain the necessary totals by combining the information with DATA2.

Answer 2

To improve efficiency, I suggest creating a second table named DATA2 that includes a single row for each month with the number equal to zero. Instead of querying data from the table DATA alone, you can achieve the desired results by querying from a combined dataset:

FROM (SELECT * FROM DATA 
UNION ALL 
SELECT * FROM DATA2) D

By following this approach, you can ensure that even when there are no values for a specific month in DATA, you will still obtain the necessary totals by combining the information with DATA2.

Answer 3

Answer №2

Below is an example without using a temporary table. Instead, it utilizes the sequence ENGINE. The main distinction is that you need to input the start date and the count of months (seq_0_to_4).

SELECT `DATE`, SUM(number) as number
FROM (
  SELECT
    date_format( IF(d.`DATE` IS NULL, init.`DATE`, d.`DATE`) ,'%Y-%m') AS `DATE`
    , IF(d.number IS NULL,0,d.number) as number
  FROM (
    SELECT '2015-01-01' + INTERVAL seq MONTH AS `DATE`, 0 AS number
    FROM seq_0_to_4
    ) AS INIT
  LEFT JOIN DATA d ON date_format(d.`DATE`,'%Y-%m') = date_format( init.`DATE` ,'%Y-%m')
  ) AS result
GROUP BY `DATE`
ORDER BY `DATE`;

Output

+---------+--------+
| DATE    | number |
+---------+--------+
| 2015-01 |      7 |
| 2015-02 |      0 |
| 2015-03 |      7 |
| 2015-04 |      0 |
| 2015-05 |      0 |
+---------+--------+
5 rows in set (0.00 sec)

Data Table

MariaDB > select * from data;
+------------+--------+
| date       | number |
+------------+--------+
| 2015-01-01 |      4 |
| 2015-01-02 |      3 |
| 2015-03-05 |      7 |
+------------+--------+
3 rows in set (0.00 sec)

MariaDB >

Answer 4

Below is an example without using a temporary table. Instead, it utilizes the sequence ENGINE. The main distinction is that you need to input the start date and the count of months (seq_0_to_4).

SELECT `DATE`, SUM(number) as number
FROM (
  SELECT
    date_format( IF(d.`DATE` IS NULL, init.`DATE`, d.`DATE`) ,'%Y-%m') AS `DATE`
    , IF(d.number IS NULL,0,d.number) as number
  FROM (
    SELECT '2015-01-01' + INTERVAL seq MONTH AS `DATE`, 0 AS number
    FROM seq_0_to_4
    ) AS INIT
  LEFT JOIN DATA d ON date_format(d.`DATE`,'%Y-%m') = date_format( init.`DATE` ,'%Y-%m')
  ) AS result
GROUP BY `DATE`
ORDER BY `DATE`;

Output

+---------+--------+
| DATE    | number |
+---------+--------+
| 2015-01 |      7 |
| 2015-02 |      0 |
| 2015-03 |      7 |
| 2015-04 |      0 |
| 2015-05 |      0 |
+---------+--------+
5 rows in set (0.00 sec)

Data Table

MariaDB > select * from data;
+------------+--------+
| date       | number |
+------------+--------+
| 2015-01-01 |      4 |
| 2015-01-02 |      3 |
| 2015-03-05 |      7 |
+------------+--------+
3 rows in set (0.00 sec)

MariaDB >

SQL - Retrieve information for a specified time frame using a predetermined value

Answer №1

Answer №2

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