Closest Saturday less than or equal to a date given

Digg This!     StumbleUpon     Del.icio.us

RELATED CONTENT SQL How to check SQL query construction with the Mimer Validator Using the SQL GROUP BY clause for counting combinations How to use an SQL CASE expression How to sort an SQL UNION query with special ORDER BY sequence How to use string functions to make an SQL join An SQL solution for a customer order homework problem How to use SQL's POSITION function with substrings Using SQL date functions to get totals for last three days Using CASE in the SQL ORDER BY clause What's the difference between an SQL inner join and equijoin? Oracle and SQL Using the SQL GROUP BY clause for counting combinations How to use an SQL CASE expression How to use the Oracle Database SQL Reference Manual How to use SQL Developer to run SQL statements How to work with the Oracle database home page How to use SQL*Plus in Oracle How to use SQL Developer to work with an Oracle database How to view and edit table column definitions How to sort an SQL UNION query with special ORDER BY sequence How to use string functions to make an SQL join Oracle and SQL Research

RELATED GLOSSARY TERMS Terms from Whatis.com − the technology online dictionary autonomous transaction  (SearchOracle.com) CFML  (SearchOracle.com) dynamic SQL  (SearchOracle.com) foreign key  (SearchOracle.com) Java Database Connectivity  (SearchOracle.com) Open Database Connectivity  (SearchOracle.com) Oracle  (SearchOracle.com) stored procedure  (SearchOracle.com) The Open Group  (SearchOracle.com)

RELATED RESOURCES 2020software.com, trial software downloads for accounting software, ERP software, CRM software and business software systems Search Bitpipe.com for the latest white papers and business webcasts Whatis.com, the online computer dictionary

My approach would be to take the day of the week of the given date, use this to come up with a number between 0 and 6, and subtract this number of days from the given date. This is basically all there is to it, except for minor implementation details.

The details consist in whether Saturday is the seventh day of your week or the sixth, and then finding the right date function(s) in your particular database system to yield the day of week. Most likely there will be some DATEPART or EXTRACT function.

For example, MySQL has two: WEEKDAY(date) returns the weekday index 0=Monday, 1=Tuesday, ... 6=Sunday), while DAYOFWEEK(date) returns the weekday index 1=Sunday, 2=Monday, ..., 7=Saturday. Using the latter function, as well as the MOD (modulo) function (to change 7 to 0, because you said "closest saturday less than or equal to a date given")...

select inputdate 
     , date_sub(inputdate
         , interval 
             mod(dayofweek(inputdate),7) 
               day ) as saturday
  from (
       select '2007-01-01' as inputdate
       union all select '2007-02-23'
       union all select '2007-02-24'
       union all select '2007-02-25'
       union all select '2007-02-26'
       union all select '2007-02-27'
       union all select '2007-02-28'
       union all select '2007-03-01'
       union all select '2007-03-02'
       union all select '2007-03-03'
       union all select '2007-03-04'
       ) as d
        
inputdate  saturday
2007-01-01 2006-12-30
2007-02-23 2007-02-17
2007-02-24 2007-02-24
2007-02-25 2007-02-24
2007-02-26 2007-02-24
2007-02-27 2007-02-24
2007-02-28 2007-02-24
2007-03-01 2007-02-24
2007-03-02 2007-02-24
2007-03-03 2007-03-03
2007-03-04 2007-03-03

Neat, eh?