Specific SQL query for invariant locales - sql

Question

I have a table with the same descriptions on many languages for one object. I need to construct a select query to get one needed description having user locale, invariant locale, and if any of the locales will not match with data in the table get one random record.
+---+----+--------+--------+-------------+
| | id | locale | object | description |
+---+----+--------+--------+-------------+
| 1 | 1 | it | cat | gatto |
| 2 | 2 | pl | cat | kot |
| 3 | 3 | de | cat | Katze |
| 4 | 4 | en | cat | cat |
+---+----+--------+--------+-------------+
If user locale is 'it' and the default is 'en', must return -> gatto;
If user locale is 'ru' and the default is 'en', must return -> cat;
If user locale is 'ru' and the default is 'po', must return -> any record;
Do you know any variant of query which can do that thing?

Answer 1

You could use coalesce() and conditional aggregation as follows:
select
coalesce(
max(case when locale = :user_locale then description end),
max(case when locale = :default_locale then description end)
)
from mytable
where object = 'cat'
Where :user_locale is the parameter that contains the user locale and :default_locale contains the default locale.

Answer 2

First thing you should do is split the table in three entity to avoid redondance in the column "object" AND to avoid violating 3rd normal form (with column "object" and "description" being in functional dependence with locale wich is not the key).
So you will have the following table :
Locale(id_locale, locale)
-->id_locale is primary key
Object(id_object, code)
--> id_object is primary key
Locale_Tran(id_locale,id_object, description)
--> (id_locale, id_object) is composed primary key
--> id_locale is foreign key references on Locale(id_locale)
--> id_object is foreign key references on Object(id_object)
(I choose the name for the table but of course you can adapt it to your actual model)
CREATE DATABASE TEST
USE TEST
CREATE TABLE [LOCALE]
(
id_locale INT IDENTITY(1,1),
locale CHAR(2),
CONSTRAINT pk_locale PRIMARY KEY(id_locale)
);
CREATE TABLE [USER]
(
id INT IDENTITY(1,1),
locale INT NOT NULL,
CONSTRAINT fk_user_locale FOREIGN KEY(locale) REFERENCES LOCALE(id_locale)
);
CREATE TABLE [OBJECT]
(
id_object INT IDENTITY(1,1),
code VARCHAR(100),
CONSTRAINT pk_object PRIMARY KEY(id_object)
);
CREATE TABLE [LOCALE_TRAN]
(
id_locale INT,
id_object INT,
[description] VARCHAR(200) NOT NULL,
CONSTRAINT fk_tran_locale FOREIGN KEY(id_locale) REFERENCES [LOCALE](id_locale),
CONSTRAINT fk_locale_object FOREIGN KEY(id_object) REFERENCES [OBJECT](id_object),
CONSTRAINT pk_locale_tran PRIMARY KEY(id_locale, id_object)
)
INSERT INTO LOCALE
(locale)
VALUES
('IT'),
('FR'),
('PL'),
('DE'),
('EN'),
('RU');
INSERT INTO [USER]
(locale)
VALUES
(2),
(3),
(4),
(5),
(6),
(6),
(1)
INSERT INTO [OBJECT]
(code)
VALUES
('CAT'),
('FISH');
INSERT INTO [LOCALE_TRAN]
VALUES
(1,1,'gatto'),
(2,1,'chat'),
(3,1,'kot'),
(4,1,'katze'),
(5,1,'cat'),
(1,2,'pesce')
Here is the query :
DROP PROCEDURE IF EXISTS dbo.getTran
GO;
CREATE PROCEDURE dbo.getTran
(
#userLocale CHAR(2),
#defaultLocale CHAR(2),
#objectId INT
)
AS
SELECT #userLocale = (SELECT id_locale FROM LOCALE l WHERE l.locale = #userLocale);
SELECT #defaultLocale = (SELECT id_locale FROM LOCALE l WHERE l.locale = #defaultLocale);
SELECT
coalesce(
max(case when id_locale = #userLocale then [description] end),
max(case when id_locale = #defaultLocale then [description] end)
)
FROM
(
SELECT lt.id_locale, lt.[description]
FROM [LOCALE_TRAN] lt WHERE lt.id_object = #objectId
) AS t
GO;
EXEC dbo.getTran 'FR','EN', '1'
I don't really found how to have the random locale and i didn't really understand why you wanna do that... But i will try.

Answer 3

Apply your conditions inside CTEs with the use of NOT EXISTS:
with
cte1 as (select description from tablename where locale = ParamLocale),
cte2 as (
select t.description from tablename t
where t.locale = ParamDefault
and not exists (select 1 from cte1)
),
cte3 as (
select * from cte1
union all
select * from cte2
)
select description from cte3
union all
select * from (
select description from tablename
where not exists (select 1 from cte3)
order by random() limit 1
)
Change ParamLocale and ParamDefault with your parameters.
See the demo.