MySql Self-Referencing query

Question

I have a following table named [clients] with columns and values as follows:

+--------+-----------+--------------+----------------+
| uid    | client_id | client_input |  input_value   |
+--------+-----------+--------------+----------------+
| 1      |   22      |  City        |  Seattle       |
+--------+-----------+--------------+----------------+
| 2      |   45      |  City        |  Ojai          |
+--------+-----------+--------------+----------------+
| 3      |   22      |  State       |  OR            |
+--------+-----------+--------------+----------------+
| 4      |   45      |  State       |  CA            |
+--------+-----------+--------------+----------------+
| 5      |   65      |  City        |  Orlando       |
+--------+-----------+--------------+----------------+
| 6      |   74      |  State       |  AB            |
+--------+-----------+--------------+----------------+
| 7      |   65      |  State       |  FL            |
+--------+-----------+--------------+----------------+
| 8      |   12      |  City        |  Los Angeles   |
+--------+-----------+--------------+----------------+
| 9      |   12      |  State       |  CA            |

I need PHP/MySql query which would list all the cities present in the input_value column which are located in the state of 'CA'. Obviously the common identifier is the client_id which is always a match because if client is in 'Los Angeles' the same client_id is also in the row which contains the value of 'CA' in the input_value column. This table has over 8 million rows and any fast performing equerry is highly appreciated.

My brain fried, deadline approaching, can't change the table design, need help, please!

Answer 1

SELECT *
FROM table AS t1 INNER JOIN table AS t2 ON t1.client_id = t2.client_id
WHERE t1.client_input = 'City' AND t2.client_input = 'State' AND t2.input_value = 'CA'

Note: This may need some adjustments and could likely be optimized. But it should get you started and cool your brain.

Answer 2

I did not tested this query. But this or a similar query should work. I first used two subqueries to avoid unecessary joins. The first subquery filters for the state 'CA' and the second subquery for cities. If you want a table for all cities by their state, remove the 'CA' clause from subquery a.

SELECT b.input_value AS city, a.input_value AS state
FROM 
  (SELECT client_id, input_value
   FROM tablename
   WHERE input_value = 'CA'
   AND client_input = 'State')
  AS a,
  (SELECT client_id, input_value
   FROM tablename
   WHERE client_input = 'City')
  AS b
WHERE a.client_id = b.client_id

Answer 3

SELECT distinct 
      t2.Input_Value as City
   from
      YourTable t1
         JOIN YourTable t2
            on t1.client_ID = t2.Client_ID
           AND t2.client_input = 'City'
   where
          t1.client_input = 'State'
      AND t1.Input_Value = 'CA'

I would have two indexes... (Client_Input, Input_Value) and (Client_ID, Client_Input, Input_Value)