Ordering values by custom criteria - mysql

Question

I have two tables A and B table:
Table - A - represents basic information of persons
emp_id | email | name
----------------------------------------
1 | abc#gmail.com | john
2 | dbc#gmail.com | john1
3 | cbc#gmail.com | john2
4 | xbc#gmail.com | john3
5 | xac#gmail.com | john4
Table - B represents the locations handled by persons
john is handling Region and Zone
john1 is handling Area and Territory and so on...
Sequence of locationType is as follows : Region->Zone->Area->Territory
Regions is having higher priority then comes zone and so on..
id | emp_id | locationType
--------------------
1 | 1 | Region
2 | 2 | Area
3 | 3 | Area
4 | 4 | Territory
5 | 1 | Zone
6 | 2 | Territory
7 | 5 | Zone
8 | 5 | Area
I want to fetch those persons who are handling the higher locationType.
Suppose john is handling Region and zone so i want to display Region as Region is of higher priority and similarly john1 is handling Territory and Area so i want to display only Area as because Area is of higher priority
My Desired Output:
id | emp_id | name | locationType
----------------------------------------
1 | 1 | john | Region
5 | 5 | john4 | Zone
3 | 3 | john1 | Area
4 | 4 | john2 | Area
4 | 4 | john3 | Territory
What I am getting
id | emp_id | name | locationType
----------------------------------------
1 | 1 | john | Region
1 | 1 | john | Zone
5 | 5 | john4 | Zone
5 | 5 | john4 | Area
2 | 2 | john1 | Area
3 | 3 | john2 | Area
4 | 4 | john3 | Territory
4 | 4 | john3 | Territory

Answer 1

You can use field() to turn the locations into numbers. What you want is the minimum location based on this ordering.
You can obtain this information per employee using a correlated subquery:
select b.*
from b
where field(b.locationType, 'Region', 'Zone', 'Area', 'Territory') =
(select min(field(b2.locationType, 'Region', 'Zone', 'Area', 'Territory'))
from b b2
where b2.emp_id = b.emp_id
);
Adding the extra columns from a is just a matter of joining in the table.

Answer 2

use case when in order clause
order by (case locationType when 'Region' then 1
when 'Zone' then 2
when 'Area' then 3
when 'Territory' then 4
else 5 end )

Answer 3

To Resolve the Issue Pemanently just Follow the following steps. It will help you in data normalization also.
1 Create A new table that has LocaitonType name and id and Insert your location type as the order you want.
CREATE TABLE [dbo].[Table_C](
[LocationType_Id] [int] IDENTITY(1,1) NOT NULL,
[name] [nvarchar](50) NULL )
Insert Into [Table_C] (name) values('Region')
Insert Into [Table_C] (name) values('Zone')
Insert Into [Table_C] (name) values('Area')
Insert Into [Table_C] (name) values('Territory')
2.Alter your table b LocationType column Data type to int.
Alter Table Table_B
Alter column locationType int not null
Now Insert id from Table_c to Table_B Locationtype Column.
and use the below query to get the desired output.
Select Table_B.id,Table_A.emp_id,Table_A.name,Table_C.name as locationType from Table_B inner join Table_A on Table_A.emp_id=Table_B.emp_id
inner join Table_C on Table_C.LocationType_Id=Table_B.locationType
order by Table_C.LocationType_Id