SQL联合与具有不同类型的表

Question

I have the following tables, in which I store the properties of my application (FYI I'm not directly using SQL in my app but Python Django which allows me to have a structure like that):

      string_properties
 id  |  name         | value (type=string)
  1  :  module.ip    : "127.0.0.1"
  2  :  module.name  : "a_name"
     :               :

      integer_properties
 id  |  name       | value (type=integer)
  1  : module.size : 10
  2  : module.port : 80
     :             :

      boolean_properties
 id  |  name             | value (type=bool)
  1  : module.activated  : 1
     :                   :

And I would like to generate a view which shows for each property, the value associated.

I tried several strategies to do so:

1- using a basic UNION: it didn't work as the "value" column isn't the same type in all my tables

2- changing the names of the "value" column, adding a suffix to it (like value_int, value_string, etc). Then I would have expected to be able to use an UNION statement but it failed too. I would be happy with a result table like below:

      result
 id  |  name             | value_int | value_string | value_bool
  1  :  module.ip        :     null  : "127.0.0.1"  : null
  2  :  module.name      :     nulll : "a_name"     : null
  3  : module.activated  :     null  :  null        :  1
  4  : module.size       :      10   :  null        : null
  5  : module.port       :      80   :  null        : null
     :                   :

3- I guess I could convert all my values to string and then UNION the table, but it's ugly to lose the types.

What do you think?

Answer 1

SELECT id, name, value AS value_int, null AS value_string, null AS value_bool
FROM integer_properties
UNION ALL
SELECT id, name, null AS value_int, value AS value_string, null AS value_bool
FROM string_properties
UNION ALL
SELECT id, name, null AS value_int, null AS value_string, value AS value_bool
FROM boolean_properties

Answer 2

I'd suggest using a UNION ALL as you suggest, and casting the values.

SELECT 
    id, 
    name, 
    value
FROM
    string_properties
UNION ALL 
SELECT 
    id, 
    name, 
    CAST(value AS CHAR(50)) AS value
FROM
    integer_properties
UNION ALL 
SELECT 
    id, 
    name, 
    CAST(value AS CHAR(50)) AS value
FROM
    boolean_properties

If you want to know where a value came from you could add a fourth column - eg SELECT "string_properties" AS parent_table among the other fields from that table (and do the same for the other tables, with a different string value, also calling it parent_table )

Answer 3

If you "don't want to lose the types", you can select the underlying type as a constant in the UNION :

CREATE VIEW all_properties AS
SELECT id, name, typ, value
FROM    (
        SELECT sp.id AS id
        , sp.name AS name
        , 'String' AS typ
        , sp.value AS value
        FROM string_properties sp
UNION ALL
        SELECT ip.id AS id
        , ip.name AS name
        , 'Integer' AS typ
        , ip.value::varchar AS value
        FROM integer_properties ip
UNION ALL
        SELECT bp.id AS id
        , bp.name AS name
        , 'Boolean' AS typ
        , bp.value::varchar AS value
        FROM boolean_properties bp
        ) x
        ;
SELECT * FROM all_properties ap
ORDER BY id,name
        ;