CODEWITHSUNDEEP
sql-servert-sql
PRHMN
PRHMN

Reputation: 119

SQL SELECT Query with returning hierarchical data

I have got a table which goes something like this: 

State_id | County_id|  City_id |     Name      |    Additional_Name
-----------------------------------------------------------------
   1     |     0    |     0    |   California  |        State
   1     |     1    |     0    |   Los Angeles |        County
   1     |     1    |     1    |   Los Angeles |        City
   1     |     2    |     0    |   San Diego   |        County
   1     |     2    |     1    |   San Diego   |        City
   2     |     0    |     0    |   Texas       |        State
   2     |     1    |     0    |   Harris      |        County
   2     |     1    |     1    |   Houston     |        City

It goes on for 10,000 rows. What I'm trying to accomplish is to build a SELECT statement which will result in:

  State       |   County     |     City
 -------------------------------------------
  California  |  Los Angeles |    Los Angeles
  California  |  San Diego   |    San Diego
  Texas       |  Harris      |    Houston

As you can see i want to select every city and display it's state, and county. The state_id, county_id, city_id and Additonal_Name columns should be essential in solving this problem, but i have no idea how to use them.

Upvotes: 0

Views: 78

Answers (1)

arserbin3
arserbin3

Reputation: 6148

This will get your data, using your current table structure:

SELECT t2.[Name] AS [State]
    ,t3.[Name] AS County
    ,t1.[Name] AS City
FROM MyTable t1
JOIN MyTable t2 -- get state
    ON t2.State_id = t1.State_id
       AND t2.County_id = 0
       AND t2.City_id = 0
JOIN MyTable t3 -- get county
    ON t3.County_id = t1.County_id
       AND t3.State_id = t1.State_id
       AND t3.City_id = 0
WHERE t1.City_id > 0 --(or use t1.Additional_Name = 'City'

But Really:

You should be normalizing your database into three separate tables:

  1. City
  2. State
  3. County

This will make using your data, and writing queries - muchh simpler and readable.

The tables would look something like this:

State

ID Name
 1 California
 2 Texas

County

ID Name
 1 Los Angeles
 2 San Diego
 3 Harris

City

ID StateID CountyID Name
 1 1       1        Los Angeles
 2 1       2        San Diego
 3 2       3        Houston

Hopefully you can see how much easier that is to manage things. You can choose to add a StateID to the County table to normalize further. But I'll keep my answer short.

Select the same data from these new tables with a similar query:

SELECT state.[Name] AS [State]
    ,county.[Name] AS County
    ,city.[Name] AS City
FROM MyCity city
JOIN MyState state ON state.ID = city.StateID -- get state
JOIN MyCounty county ON county.ID = city.CountyID -- get county

Upvotes: 2

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