SQL组仅按相关行

Question

Say I have the following table:

Code A  B  C Date       ID
------------------------------
50   1  1  A 2018-01-08 150001  
50   1  1  A 2018-01-15 165454  
50   1  1  B 2018-02-01 184545  
50   1  1  A 2018-02-02 195487

I need the sql query to output the following:

Code A  B  C Min(Date)  Min(ID)
-------------------------------
50   1  1  A 2018-01-08 150001
50   1  1  B 2018-02-01 184545
50   1  1  A 2018-02-02 195487

If I use standard group by, rows 1,2,4 are grouped in 1 row, and this is not that I want. I want to select the row with MIN(date) and MIN(id) from the duplicate records that are together based on column code, A, B and C in this case 1st 2 rows are duplicates so i want the min() row. and 3rd and 4th row are distinct.

Note that the database is Vertica 8.1, that is very similar to Oracle or PostgreSQL

Answer 1

I think you would need the analytic function LAG() . Using this function, you can get the value of the previous row (or NULL if it's the first row itself). So you can check if the value on the previous row is different or not, and filter accordingly.

I'm not familiar with Vertica, but this should be the correct documentation for it: https://my.vertica.com/docs/7.0.x/HTML/Content/Authoring/SQLReferenceManual/Functions/Analytic/LAGAnalytic.htm

Please try the query below, it should do it:

SELECT l.Code, l.A, l.B, l.C, l.Date, l.ID
  FROM (SELECT t.*,
               LAG(t.C, 1) OVER (PARTITION BY t.Code, t.A ORDER BY t.Date) prev_val
          FROM table_1 t) l
 WHERE l.C != l.prev_val
    OR l.prev_val IS NULL
 ORDER BY l.Code, l.A, l.Date