sql query to find potential duplicate records - mysql

Question

I am working on employer's data to find out duplicate employers based on their names.
Data is Like this:
Employer ID | Legal Name | Operating Name
------------- | ---------------| --------------------
1 | AA | AA
2 | BB | AA
3 | CC | BB
4 | DD | DD
5 | ZZ | ZZ
Now if I try to find all duplicates of employer AA the query should return the following result:
Employer ID | Legal Name | Operating Name
------------- | ---------------| --------------------
1 | AA | AA
2 | BB | AA
3 | CC | BB
Employer 1's legal name and Employer 2's Operating Name are the direct match with the search.
But the catch is employer 3 which is not directly related with the search string but employer 2's legal name matches with employer 3's operating name.
And I need the search results up to nth level. I am not sure if that can be achieved by recursive query of something like that.
Please help
I was trying to achieve this by Recursive CTE but then I realized that it is going into infinite recursion. Here is the code:
DECLARE #SearchName VARCHAR(50)
SET #SearchName = 'AA'
;With CTE_EmployerNames
AS
(
-- Anchor Member definition
select *
from [dbo].[Name_Table]
where Leg_Name = #SearchName
OR Op_Name = #SearchName
UNION ALL
-- Recursive Member definition
select N.*
from [dbo].[Name_Table] N
JOIN CTE_EmployerNames C
ON N.ID <> C.ID
AND (N.Leg_Name = C.Leg_Name
OR N.Leg_Name = C.Op_Name
OR N.Op_Name = C.Leg_Name
OR N.Op_Name = C.Op_Name)
)
select *
from CTE_EmployerNames
Update:
I created a stored procedure to achieve what I want. But this procedure is a bit slow because of looping and cursor. As of now this is solving my problem by little compromising with execution time. Any suggestion to optimize it or another way to do this will be highly appreciated. thanks guys. Here is the code:
CREATE PROCEDURE [dbo].[Get_Similar_Name_Employers]
#P_BaseName VARCHAR(100)
AS
BEGIN
DECLARE #ID INT
DECLARE #Leg_Name VARCHAR(50)
DECLARE #Op_Name VARCHAR(50)
-- Create temp table to hold data temporarily
CREATE TABLE #Temp_Employers
(
[ID] [int] NULL,
[Leg_Name] [varchar](50) NULL,
[Op_Name] [varchar](50) NULL,
[Status] [bit] null -- To keep track if that record is processed or not
)
-- Insert all records which are directly matching with search criteria
INSERT INTO #Temp_Employers
SELECT NT.ID, NT.Leg_Name, NT.Op_Name, 0
FROM dbo.Name_Table NT
WHERE NT.Leg_Name = #P_BaseName
OR NT.Op_Name = #P_BaseName
while EXISTS (SELECT 1 from #Temp_Employers where Status = 0) -- until all rows are processed
BEGIN
DECLARE #EmployerCursor CURSOR
SET #EmployerCursor = CURSOR FAST_FORWARD
FOR
SELECT ID, Leg_Name, Op_Name
from #Temp_Employers
where Status = 0
OPEN #EmployerCursor
FETCH NEXT
FROM #EmployerCursor
INTO #ID, #Leg_Name, #Op_Name
WHILE ##FETCH_STATUS = 0
BEGIN
-- For every unprocessed record in temp table check if there is any possible duplicate.
-- and insert all possible duplicate records in same table for further processing to find their possible duplicates
INSERT INTO #Temp_Employers
select ID, Leg_Name, Op_Name, 0
from dbo.Name_Table
WHERE (Leg_Name = #Leg_Name
OR Op_Name = #Op_Name
OR Leg_Name = #Op_Name
OR Op_Name = #Leg_Name)
AND ID NOT IN ( select ID
FROM #Temp_Employers)
-- Update status of recently processed record to avoid processing again
UPDATE #Temp_Employers
SET Status = 1
WHERE ID = #ID
FETCH NEXT
FROM #EmployerCursor
INTO #ID, #Leg_Name, #Op_Name
END
-- close cursor and deallocate memory
CLOSE #EmployerCursor
DEALLOCATE #EmployerCursor
END
select ID,
Leg_Name,
Op_Name
from #Temp_Employers
Order By ID
DROP TABLE #Temp_Employers
END

Answer 1

You are basically trying to build a directed acyclic graph in which the nodes are names and you want to find all the names that lead to your employee.
There is a beginning tutorial at Oracle Tip: Solving directed graph problems with SQL, part 1, and a related StackOverflow question at Directed graph SQL.

Answer 2

You can do this with two self joins. I used DISTINCT to be safe - you don't need it for your example, but probably will for your actual data:
SELECT DISTINCT T2.EMPID, T2.LEGAL_NAME, T.LEGAL_NAME
FROM TABLE T
INNER JOIN TABLE T2 ON T.LEGAL_NAME = T2.OPERATING_NAME
INNER JOIN TABLE T3 ON T2.OPERATING_NAME = T3.OPERATING_NAME
WHERE T.LEGAL_NAME <> T3.LEGAL_NAME
Rename and alias tables and columns as you like.
SQL Fiddle Example
Edit - If you also want records where the op name is simply different from the legal name, UNION those in:
SELECT DISTINCT T2.EMPID, T2.LEGAL_NAME, T.LEGAL_NAME
FROM TABLE T
INNER JOIN TABLE T2 ON T.LEGAL_NAME = T2.OPERATING_NAME
INNER JOIN TABLE T3 ON T2.OPERATING_NAME = T3.OPERATING_NAME
WHERE T.LEGAL_NAME <> T3.LEGAL_NAME
UNION
SELECT EMPID, LEGAL_NAME, OP_NAME
FROM TABLE
WHERE LEGAL_NAME <> OP_NAME
SQL Fiddle Example 2