How to Generate Months within a Specific Date Range in MySQL, Including Empty Values?

Generating Months within Specific Date Range, Including Empty Values

Question:

In MySQL, how can I generate a list of all months within a given date range, even if no values exist for some months?

Answer:

To achieve this, create a separate table containing all possible months, such as:

CREATE TABLE dateTable (
  myDate DATE NOT NULL,
  myYear SMALLINT NOT NULL,
  myMonth TINYINT UNSIGNED NOT NULL
);

Populate this table with all the months you may encounter in your data.

Then, use a LEFT JOIN to combine your original table, myTable, with the dateTable:

SELECT DT.myYear, DT.myMonth, 
       AVG(myTable.value1) AS avg_value_1, 
       AVG(myTable.value2) AS avg_value_2
FROM dateTable AS DT
LEFT JOIN myTable
  ON DT.myDate = myTable.save_date
WHERE DT.myDate BETWEEN '2009-01-01' AND '2009-07-01'
GROUP BY DT.myYear, DT.myMonth

This will retrieve average values for all months within the specified range, including months with no values in myTable. The LEFT JOIN ensures that empty values are included by matching DT.myDate to all rows in myTable, regardless of whether they have corresponding values.

You can further customize the output by adjusting the GROUP BY clause to group results by desired time periods, such as financial quarters or days of the week. This approach provides a convenient and efficient way to generate comprehensive reports with complete month coverage.

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