How Can I Extract the Week Number from a Date in SQL?

Extracting Week Number from Date in SQL

The task of extracting the week number from a date can be encountered when working with timestamp data in relational databases. Here's how to achieve this using SQL, addressing an issue faced by a user in extracting week numbers from date values.

The provided date values are in the format of 'MM/DD/YYYY' and were converted to a true date datatype using the TO_DATE function. However, attempting to extract the week number using TO_CHAR(TO_DATE(TRANSDATE), 'w') resulted in null values.

To successfully extract the week number, you need to convert the converted date back to a string format using a specific mask.

TO_CHAR(TO_DATE('01/02/2012', 'MM/DD/YYYY'), 'WW')

This expression utilizes the 'WW' mask, which represents the week of the year (1-53). You can also use other options such as 'W' for the week of the month or 'IW' for the ISO week number.

If you prefer a numeric week number, surround the statement with the TO_NUMBER function:

TO_NUMBER(TO_CHAR(TO_DATE('01/02/2012', 'MM/DD/YYYY'), 'WW'))

Keep in mind that the extracted week number corresponds to the specified parameter:

• 'WW': Week of year (1-53), starting on the first day of the year
• 'W': Week of month (1-5), starting on the first day of the month
• 'IW': ISO week of year (1-52 or 1-53)

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