SELECT DISTINCT is not working - sql

Question

Let's say I have a table name TableA with the below partial data:
LOOKUP_VALUE LOOKUPS_CODE LOOKUPS_ID
------------ ------------ ----------
5% 120 1001
5% 121 1002
5% 123 1003
2% 130 2001
2% 131 2002
I wanted to select only 1 row of 5% and 1 row of 2% as a view using DISTINCT but it fail, my query is:
SELECT DISTINCT lookup_value, lookups_code
FROM TableA;
The above query give me the result as shown below.
LOOKUP_VALUE LOOKUPS_CODE
------------ ------------
5% 120
5% 121
5% 123
2% 130
2% 131
But that is not my expected result, mt expected result is shown below:
LOOKUP_VALUE LOOKUPS_CODE
------------ ------------
5% 120
2% 130
May I know how can I achieve this without specifying any WHERE clause?
Thank you!

Answer 1

I think you're misunderstanding the scope of DISTINCT: it will give your distinct rows, not just distinct on the first field.
If you want one row for each distinct LOOKUP_VALUE, you either need a WHERE clause that will work out which one of them to show, or an aggregation strategy with a GROUP BY clause plus logic in the SELECT that tells the query how to aggregate the other columns (e.g. AVG, MAX, MIN)

Answer 2

Here's my guess at your problem - when you say
"The above query give me the result as shown in the data table above."
this is simply not true - please try it and update your question accordingly.
I am speculating here: I think you are trying to use "Distinct" but also output the other fields. If you run:
select distinct Field1, Field2, Field3 ...
Then your output will be "one row per distinct combination" of the 3 fields.
Try GROUP BY instead - this will let you select the Max, Min, Sum of other fields while still yielding "one row per unique combined values" for fields included in GROUP BY
example below uses your table to return one row per LOOKUP_VALUE and then the max and min of the remaining fields and the count of total records using your data:
select
LOOKUP_VALUE, min( LOOKUPS_CODE) LOOKUPS_CODE_min, max( LOOKUPS_CODE) LOOKUPS_CODE_max, min( LOOKUPS_ID) LOOKUPS_ID_min, max( LOOKUPS_ID) LOOKUPS_ID_max, Count(*) Record_Count
From TableA
Group by LOOKUP_VALUE

Answer 3

I wanted to select only 1 row of 5% and 1 row of 2%
This will get the lowest value lookups_code for each lookup_value:
SELECT lookup_value,
lookups_code
FROM (
SELECT lookup_value,
lookups_code,
ROW_NUMBER() OVER ( PARTITION BY lookup_value ORDER BY lookups_code ) AS rn
FROM TableA
)
WHERE rn = 1
You could also use GROUP BY:
SELECT lookup_value,
MIN( lookups_code ) AS lookups_code
FROM TableA
GROUP BY lookup_value

Answer 4

How about the MIN() function
I believe this works for your desired output, but am currently not able to test it.
SELECT Lookup_Value, MIN(LOOKUPS_CODE)
FROM TableA
GROUP BY Lookup_Value;

Answer 5

I'm going to take a total shot in the dark on this one, but because of the way you have named your fields it implies you are attempting to mimic the vlookup function within Microsoft Excel. If this is the case, the behavior when there are multiple matches is to pick the first match. As arbitrary as that sounds, it's the way it works.
If this is what you want, AND the first value is not necessarily the lowest (or highest, or best looking, or whatever), then the row_number aggregate function would probably suit your needs.
I give you a caveat that my ordering criteria is based on the database row number, which could conceivably be different than what you think. If, however, you insert them into a clean table (with a reset high water mark), then I think it's a pretty safe bet it will behave the way you want. If not, then you are better off including a field explicitly to tell it what order you want the choice to occur.
with cte as (
select
vlookup_value,
vlookups_code,
row_number() over (partition by vlookup_value order by rownum) as rn
from
TableA
)
select
vlookup_value, vlookups_code
from cte
where rn = 1