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Question

My original database looks like that:

TYPE CONTRACT_ID
a    101011 
c    101012
b    101011
b    101012
a    101011-1
c    101012

I am trying to get data, grouped by TYPE, counting unique CONTRACT_ID, but some contracts have subcontracts, like 101011 has subcontract 101011-1. All of them have to be counted as one contract.

I have tried distinct and it works but only partially because those subcontracts still being counted as unique entrees.

SELECT TYPE, count(distinct CONTRACT_ID) as countocc
FROM db_address
group by TYPE

I expect output like that:

TYPE  countocc
a     1 
b     2
c     1

Answer 1

How about ignoring the subcontracts all-together? You seem to have the parent contract when you have the subs:

SELECT TYPE, count(distinct CONTRACT_ID) as countocc
FROM db_address
WHERE CONTRACT_ID NOT LIKE '%-%'
GROUP BY TYPE;

Answer 2

Use a CASE statement to count only the part of contract_id before the '-' (if it exists):

select 
  type,
  count(distinct 
    case 
      when contract_id like '%-%' then 
        substring(contract_id, 1, instr(contract_id, '-') - 1)
      else contract_id
    end
  ) counter
from db_address
group by type

This covers the case (if there is such a case) that a subcontract is in the table but not the main contract.
The code works for MySql but all the functions used can be found in any rdbms.
See the demo .
Results:

| type | counter |
| ---- | ------- |
| a    | 1       |
| b    | 2       |
| c    | 1       |

Answer 3

The logic might be extracting the part of the string upto the dash character, if exists, and then grouping by type column. But method differs depending on the DBMS .

If you're using Oracle , consider :

select type, 
       count( distinct
             case when instr(contract_id,'-') > 0 then
                  substr(contract_id,1,instr(contract_id,'-')-1)
             else
                  contract_id
             end) as countocc
  from db_address d
 group by type 

If SQL Server , then consider :

select type, 
       count( distinct
             case when charindex('-',contract_id) > 0 then
                  left(contract_id,charindex('-',contract_id)-1)
             else
                  contract_id
             end) as countocc
  from db_address d
 group by type;

If MySQL , then consider :

select type, 
       count(distinct substring(contract_id,1,instr(contract_id,'-')-1)) as countocc
  from db_address d
 group by type;

If PostGRES , then consider :

select type, 
       count( distinct
             case when strpos(contract_id,'-') > 0 then
                  substr(contract_id,1,strpos(contract_id,'-')-1)
             else
                  contract_id
             end) as countocc
  from db_address d
 group by type;