SQL decode on column4 but only when column5 is distinct
Question
I need to change the sum(decode()) expressions that are like
SUM(Decode(vcon.WAGON_TYPE_CODE,'MS',1,0))
to something that counts rows with vcon.WAGON-TYPE-CODE = 'MS' but only when wag.ACI-TAG-NO is distinct.
So if two columns look like this
vcon.WAGON_TYPE_CODE wag.ACI_TAG_NO
MS HI1111
SS C99999
MS HI1111
MS HI7777
SS HI8888
MS HI6666
The expression needs to return the number 3 rather than 4 as SUM(Decode(vcon.WAGON_TYPE_CODE,'MS',1,0)) currently does.
Any suggestions?
querySELECT = "SELECT "
querySELECT = querySELECT & "trn.WID_DATE, "
querySELECT = querySELECT & "trn.MINE_CODE, "
querySELECT = querySELECT & "trn.TRAIN_CONTROL_ID, "
querySELECT = querySELECT & "trn.NUM_CARS as HBD_Car_Count, "
querySELECT = querySELECT & "SUM(Decode(vcon.WAGON_TYPE_CODE,'MS',1,0)) M_Series, "
querySELECT = querySELECT & "(SUM(Decode(vcon.WAGON_TYPE_CODE,'SS',1,0))-SUM(Decode(wag.ACI_TAG_NO,'HI0000',1,0))) S_Series, "
querySELECT = querySELECT & "SUM(Decode(vcon.WAGON_TYPE_CODE,'CS',1,0)) C_Series, "
querySELECT = querySELECT & "SUM(Decode(wag.ACI_TAG_NO,'HI0000',1,0)) as No_Tag, "
querySELECT = querySELECT & "(COUNT(1) - trn.NUM_CARS) DB_Mismatch "
queryFROM = "FROM widsys.consist con, widsys.train trn, widsys.wagon wag, widsys.v_consist_ore_detail vcon "
queryWHERE = "WHERE trn.TRAIN_RECORD_ID = con.TRAIN_RECORD_ID "
queryWHERE = queryWHERE & "AND con.WAGON_ID = wag.WAGON_ID "
queryWHERE = queryWHERE & "AND ((vcon.CONSIST_ID=con.CONSIST_ID) "
queryWHERE = queryWHERE & "AND trn.MINE_CODE In (" & mine & ") "
queryWHERE = queryWHERE & "AND (trn.DIRECTION='N') "
queryWHERE = queryWHERE & "AND (wag.ACI_TAG_TYPE In ('CONTROL','SLAVE','ORE')) "
queryWHERE = queryWHERE & "AND (trn.WID_DATE>={ts '" & startDate & "'} "
queryWHERE = queryWHERE & "AND trn.WID_DATE<={ts '" & endDate & "'})) "
queryGROUPBY = "GROUP BY trn.WID_DATE, trn.MINE_CODE, trn.TRAIN_CONTROL_ID, trn.NUM_CARS "
queryORDERBY = "ORDER BY trn.WID_DATE DESC"
Solution
I think the following should work (this count the distinct wag.ACI_TAG_NO
only when vcon.WAGON_TYPE_CODE='MS'
) :
COUNT(DISTINCT Decode(vcon.WAGON_TYPE_CODE,'MS',wag.ACI_TAG_NO,NULL))
e-g:
SQL> WITH data AS (
2 SELECT 'MS' WAGON_TYPE_CODE, 'HI1111' ACI_TAG_NO FROM DUAL UNION ALL
3 SELECT 'SS', 'C99999' FROM DUAL UNION ALL
4 SELECT 'MS', 'HI1111' FROM DUAL UNION ALL
5 SELECT 'MS', 'HI7777' FROM DUAL UNION ALL
6 SELECT 'SS', 'HI8888' FROM DUAL UNION ALL
7 SELECT 'MS', 'HI6666' FROM DUAL
8 )
9 SELECT COUNT(DISTINCT decode(WAGON_TYPE_CODE,'MS',ACI_TAG_NO,NULL))
10 FROM DATA
11 ;
COUNT(DISTINCTDECODE(WAGON_TYP
------------------------------
3
Cheers,
--
Vincent
OTHER TIPS
You could use a subquery that filters duplicate tags. Your query is pretty complex, but this would calculate just the sum you're looking for:
SELECT SUM(Decode(sub.WAGON_TYPE_CODE,'MS',1,0))
FROM (
SELECT DISTINCT vcon.WAGON_TYPE_CODE, wag.ACI_TAG_NO
FROM widsys.wagon wag
INNER JOIN widsys.consist con
ON con.wagon_id = wag.wagon_id
INNER JOIN widsys.v_consist_ore_detail vcon
ON vcon.CONSIST_ID = con.CONSIST_ID
) sub
The DISTINCT makes sure there is only one row per (wagon_type,aci_tag_no) combination.
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