What does this do?

Question

Greatest( Round( (nvl(a11.DISCH_THRU_DATE,sysdate) - a11.ADMIT_PRIMARY_DATE), 0), 0) ,
Hi can someone tell me what this does I found this in an existing report that I did not create and I am not familiar with this just a simple explaination as to the meaning. Here is what i think it does: Rounds the Disch_ Date to the highest number then subtracts the Admit_Date
but what is nvl and why the ,0),0) ? thanks

Answer 1

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Hi can someone tell me what this does I found this in an existing report that I did not create and I am not familiar with this just a simple explaination as to the meaning. Here is what i think it does: Rounds the Disch_ Date to the highest number then subtracts the Admit_Date
but what is nvl and why the ,0),0) ? thanks
>
Close - try breaking it apart and put each element on a line by itself
Greatest(
     Round(
               nvl(a11.DISCH_THRU_DATE,sysdate) - a11.ADMIT_PRIMARY_DATE
          0),
     0
     ) ,And then work from the inside out - evaluate each piece and substitute the result
nvl(a11.DISCH_THRU_DATE,sysdate) - a11.ADMIT_PRIMARY_DATEThe NVL says: if DISCH_THRU_DATE is NULL then use SYSDATE.
Then ADMIT_PRIMARY_DATE is subtracted from that date (DISCH_THRU_DATE or SYSDATE if the first is NULL).
Let's use the name 'DIFF_DATE' for the value 'DISCH date minus ADMIT_PRIMARY_DATE'
Round(
               nvl(a11.DISCH_THRU_DATE,sysdate) - a11.ADMIT_PRIMARY_DATE
          0),The above code now becomes
Round(DIFF_DATE, 0),So that Rounds the data difference to 0 places. A data difference is in days so this rounds to the nearest whole day.
Lets call that value 'WHOLE_DAYS'
Now this code
Greatest(
     Round(
               nvl(a11.DISCH_THRU_DATE,sysdate) - a11.ADMIT_PRIMARY_DATE
          0),
     0
     ) ,becomes this code
Greatest(WHOLE_DAYS, 0),So your orginal expression is calculating the number of whole days between DISCH_THRU_DATE (or sysdate if that date is NULL) and ADMIT_PRIMARY_DATE.
The 'Greatest' says to use zero if the WHOLE_DAYS is negative.