Обсуждение: Query Question

Hi All,

I have the following simplified setup. A client has 2 products: 'vbp'
and 'year_balance', but a client has also workers who have a product,
named 'ib'. A client can have multiple workers.

-- clients
CREATE TABLE clients (
    id serial NOT NULL PRIMARY KEY,
    name text NOT NULL,
    vbp boolean DEFAULT 'f'::bool NOT NULL,  -- product 'vbp'
    year_balance boolean DEFAULT 'f'::bool NOT NULL    -- product
'year_balance'
);


-- workers
CREATE TABLE workers (
    id serial NOT NULL PRIMARY KEY,
    client_id integer NOT NULL REFERENCES clients(id),
    ib boolean DEFAULT 'f'::bool NOT NULL   -- product 'ib'
);


There one thing I like to know. What products are active for a client
(clients.id) or for all clients:
I don't know what query I can use to accomplish this, but I know I would
like to have results like this

SELECT <<some_query_magic>>

clients.name | workers.ib | clients.vbp | clients.year_balance
----------------+--------------+--------------+-------------------------
 client a        |  t                |   f               | f
 client b        |  f                | t                 |  t


It is possible that a client has zero or more workers, I want to know if
one of the workers has workers.ib = 't' set if this is true I like to
have 't' returned else a 'f'

Is this possible in a single query?


Sincerely,

Frodo Larik

SELECT c.name, w.ib, c.vbp, c.year_balance
    FROM clients c
        LEFT JOIN workers w ON (w.client_id = c.id)
;

Will do the trick.

BTW, I suggest not using 'bareword' id's for field names. It's very easy
to get confused with larger queries. So instead of clients.id, do
clients.client_id. I do the same thing with name, since it's also a very
common field name, so instead of clients.name, clients.client_name.

Also, most people don't use pluralized table names. I'm guessing you're
using Ruby on Rails here...

On Tue, Sep 27, 2005 at 12:20:05PM +0200, Frodo Larik wrote:
> Hi All,
>
> I have the following simplified setup. A client has 2 products: 'vbp'
> and 'year_balance', but a client has also workers who have a product,
> named 'ib'. A client can have multiple workers.
>
> -- clients
> CREATE TABLE clients (
>    id serial NOT NULL PRIMARY KEY,
>    name text NOT NULL,
>    vbp boolean DEFAULT 'f'::bool NOT NULL,  -- product 'vbp'
>    year_balance boolean DEFAULT 'f'::bool NOT NULL    -- product
> 'year_balance'
> );
>
>
> -- workers
> CREATE TABLE workers (
>    id serial NOT NULL PRIMARY KEY,
>    client_id integer NOT NULL REFERENCES clients(id),
>    ib boolean DEFAULT 'f'::bool NOT NULL   -- product 'ib'
> );
>
>
> There one thing I like to know. What products are active for a client
> (clients.id) or for all clients:
> I don't know what query I can use to accomplish this, but I know I would
> like to have results like this
>
> SELECT <<some_query_magic>>
>
> clients.name | workers.ib | clients.vbp | clients.year_balance
> ----------------+--------------+--------------+-------------------------
> client a        |  t                |   f               | f
> client b        |  f                | t                 |  t
>
>
> It is possible that a client has zero or more workers, I want to know if
> one of the workers has workers.ib = 't' set if this is true I like to
> have 't' returned else a 'f'
>
> Is this possible in a single query?
>
>
> Sincerely,
>
> Frodo Larik
>
>
>
>
>
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--
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
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