sql select everything with maximum date (that that is smaller than a specific date) without subqueri-CodePudding

I would like to write a sql query where I choose all rows grouped by id where the column date is the latest date for this id but still smaller than for example 16-JUL-2021. I would like to do this without using subqueries (in oracle), is that possible? I tried the below but it doesn't work.

SELECT *, max(date) 
WHERE date < '16-JUL-2021'
OVER(PARTITION BY id ORDER BY date DESC) as sth
FROM table

CodePudding user response：

You can find the maximum date without sub-queries.

SELECT t.*,
       max("DATE") OVER(PARTITION BY id ORDER BY "DATE" DESC) as max_date
FROM   "TABLE" t
WHERE  "DATE" < DATE '2021-07-16'

You need a sub-query to filter to only show the row(s) with the maximum date:

SELECT *
FROM   (
  SELECT t.*,
         max("DATE") OVER(PARTITION BY id ORDER BY "DATE" DESC) as max_date
  FROM   "TABLE" t
  WHERE  "DATE" < DATE '2021-07-16'
)
WHERE  "DATE" = max_date;

However, you are still only querying the table once using this technique even though it uses a sub-query.

Note DATE and TABLE are reserved words and cannot be used as unquoted identifiers; it would be better practice to use different names for those identifiers.

You could, equivalently use the RANK or DENSE_RANK analytic functions instead of MAX; ROW_NUMBER, however, does not give the same output as it will only return a single row and will not return all tied rows.

SELECT *
FROM   (
  SELECT t.*,
         RANK() OVER(PARTITION BY id ORDER BY "DATE" DESC) as rnk
  FROM   "TABLE" t
  WHERE  "DATE" < DATE '2021-07-16'
)
WHERE  rnk = 1;

But you still need a sub-query to filter the rows.

If you want to not use a sub-query then you can use:

SELECT id,
       MAX("DATE") AS "DATE",
       MAX(col1) KEEP (DENSE_RANK LAST ORDER BY "DATE", ROWNUM) AS col1,
       MAX(col2) KEEP (DENSE_RANK LAST ORDER BY "DATE", ROWNUM) AS col2,
       MAX(col3) KEEP (DENSE_RANK LAST ORDER BY "DATE", ROWNUM) AS col3
FROM   "TABLE"
GROUP BY id

However, that is not quite the same as it will only get a single row per id and will not return multiple rows tied for the greatest date per id.