How do I do this?

[wvoyance]

my database has a table

PID language ....
1 1 ....
1 2 ......
1 3 ....
2 1 ......
2 2 ...........
etc

i.e. each PID SHOULD have language 1,2,3
The problem is some PID have some language missing i.e. only 1,3 or 1,2 etc.
I want to find out those PID with language missing.
How should I write the SQL?

[mikosiko]

one easy alternative is using GROUP_CONCAT() comparing the result with whatever string you like.
http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

[wvoyance]

one easy alternative is using GROUP_CONCAT() comparing the result with whatever string you like.
http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

oh...I forget to say...I do not know what is exactly PID is.
They are assigned by the system (for each book), and there are holes between them, i.e.
3, 4, 6, 11, 12, ...., 667, 668, 671,...
I mean, I know at best their range, i.e. starting from 1 to some large number.
I know they are integer, countable, and positive

The problem is my database is somewhat inconsistent now.
Every book (PID) should have three (1,2,3) languages. But apparently some are missing.
I need to find out which one is missing.

[VladSun]

Common solution to find non successive numeric "holes" (though it would be just the first element) in series:

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Syntax: [ Download ] [ Show ]

SELECT
  `table`.`field` + 1 AS `missing_field`
FROM
  `table`
LEFT JOIN
  `table` AS `missing_field_table` ON
      `table`.`fielld` + 1 = `missing_field_table`
WHERE
  `missing_field_table`.`field` IS NULL
 

PostgreSql has a set returning function called generate_series which is very useful in such cases - you can try implement it in MySQL and use it in a similar way as the one show above.

[wvoyance]

Common solution to find non successive numeric "holes" (though it would be just the first element) in series:

Syntax: [ Download ] [ Hide ]

Syntax: [ Download ] [ Show ]

SELECT
  `table`.`field` + 1 AS `missing_field`
FROM
  `table`
LEFT JOIN
  `table` AS `missing_field_table` ON
      `table`.`fielld` + 1 = `missing_field_table`
WHERE
  `missing_field_table`.`field` IS NULL
 

PostgreSql has a set returning function called generate_series which is very useful in such cases - you can try implement it in MySQL and use it in a similar way as the one show above.

Thank for this nice method. But this does not solve my problem.
I want to find out which PID is incomplete, i.e. do not have three language tuples 1,2,3.

I have done that by using

SELECT pid, COUNT(language) FROM products_description GROUP BY pid;

[mikosiko]

......I want to find out which PID is incomplete, i.e. do not have three language tuples 1,2,3.

as I said.... according to the objective that you are describing GROUP_CONCAT() solve your problem

Syntax: [ Download ] [ Hide ]

Syntax: [ Download ] [ Show ]

SELECT pid,
       GROUP_CONCAT(language ORDER BY language) AS the_lang
  FROM products_description
  GROUP BY pid
  HAVING the_lang != '1,2,3';

[wvoyance]

Thanks, learnt one more method. Which one will be quicker?