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Let's say that I have a range of SQL tables that are named name_YYYY_WW where YYYY = year and WW = week number. If I call upon a function that guides a user defined date to the right table.
If the date entered is "20110101":
SELECT EXTRACT (WEEK FROM DATE '20110101') returns 52 and
SELECT EXTRACT (YEAR FROM DATE '20110101') returns 2011.
While is nothing wrong with these results I want "20110101" to either point to table name_2010_52 or name_2011_01, not name_2011_52 as it does now when I concanate the results to form the query for the table.
Any elegant solutions to this problem?
558
Use the DATE_PART() function to retrieve the week number from a date in a PostgreSQL database. This function takes two arguments. The first argument is the date part to retrieve; we use 'week', which returns the week number (e.g. “1” for the first week in January, the first week of the year).
To extract the day name from the date, you can use the to_char() function. The first parameter is the date and the second is the desired output format. To extract the full day name, the format should be 'Day' : SELECT to_char( date '2022-01-01' , 'Day' );
The TO_DATE function in PostgreSQL is used to converting strings into dates. Its syntax is TO_DATE(text, text) and the return type is date. The TO_TIMESTAMP function converts string data into timestamps with timezone. Its syntax is to_timestamp(text, text) .
Use the PostgreSQL AGE() function to retrieve the interval between two timestamps or dates. This function takes two arguments: the first is the end date and the second is the start date.
The function to_char() will allow you to format a date or timestamp to output correct the iso week and iso year.
SELECT to_char('2011-01-01'::date, 'IYYY_IW') as iso_year_week;
will produce:
iso_year_week
---------------
2010_52
(1 row)
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