Get previous bill date using SQL

Question

Hi,
I am table which holds records for bill generation. I have column name gene_bill_date which is date field and it holds a value the date on which the particular bill was generated.
Now I am trying to get previous bill date, not the current bill date. I can to Max(gene_bill_date) to get current bill date, but how do I get previous bill date?
thanks

Answer 1

Hi,
Sorry, it's unclear what you're asking.
You didn't post any sample data, so I'll use the scott.emp table to illustrate. Let's say we're interested in deptno=30 only, just to reduce the output from 14 rows to 6.
If, for every row, you need to know the most recent gene_bill_date before the one on that row, you can do something like this:
SELECT     ename
,     hiredate
,     LAG (hiredate) OVER (ORDER BY hiredate)     AS prev_hiredate
FROM     scott.emp
WHERE     deptno     = 30
;Output:
ENAME      HIREDATE    PREV_HIREDA
ALLEN      20-Feb-1981
WARD       22-Feb-1981 20-Feb-1981
BLAKE      01-May-1981 22-Feb-1981
TURNER     08-Sep-1981 01-May-1981
MARTIN     28-Sep-1981 08-Sep-1981
JAMES      03-Dec-1981 28-Sep-1981Are you only interested in the 2 most recent dates in the whole result set?
If so, do a Top-N Query , like this:
WITH     got_r_num     AS
     SELECT     ename
     ,     hiredate
     ,     RANK () OVER (ORDER BY hiredate  DESC)     AS r_num
     FROM     scott.emp
     WHERE     deptno     = 30
SELECT     *
FROM     got_r_num
WHERE     r_num     <= 2
;Output:
ENAME      HIREDATE         R_NUM
JAMES      03-Dec-1981          1
MARTIN     28-Sep-1981          2 
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only), and also post the results you want from that data.
Explain, using specific examples, how you get those results from that data.
Always say which version of Oracle you're using.