How to Efficiently Extract Month and Year from VARCHAR Dates in MySQL?

Converting VARCHAR to Date in MySQL: Extracting Month and Year

In MySQL, you can encounter situations where you need to convert a VARCHAR string representing a date into a date data type. If you specifically need to extract only the month and year from the date for use in calculations, it's essential to follow the correct approach.

Using STR_TO_DATE with Proper Format

When attempting to convert a VARCHAR string to a date, using the STR_TO_DATE function is a common method. However, specifying the correct format string is crucial to avoid unexpected results.

For example, given the input string "1/9/2011," the following query:

SELECT STR_TO_DATE(CYOApp_oilChangedDate, '%m/%Y') FROM CYO_AppInfo

will not yield the desired output. This format string expects data in the form "MM/YYYY," which doesn't align with your input.

Correct Conversion

To correctly convert the input string into a date, you need to specify the correct format string as:

SELECT date_format(str_to_date('1/9/2011', '%d/%m/%Y'), '%Y%m')

This format string "%d/%m/%Y" signifies that the input string follows the "DD/MM/YYYY" format.

Alternatively, you can also use the following query:

SELECT date_format(str_to_date('12/31/2011', '%m/%d/%Y'), '%Y%m')

Note that the order of day and month in the format string should match the order in your input string.

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