Dynamic case when

Question

     SELECT
     COUNT(id), AgeRange
     FROM
     (
     select
       id,
      case
        when age < 0 then 'less than 0'
        when age >= 0 and age <=30 then '0-30'
        when age >= 31 and age <=60 then '31-60'
        when age >= 61 and age <=90 then '61-90'
        when age >= 91 then '91+'
         when age = null then 'NO INFORMATION'
      else 'no catagory'
    end AS AgeRange
 from queue 
 where DATE between '01-Apr-2011' and '05-May-2011'
 ) T
GROUP BY
    AgeRange;

I want these ageRanges (0-30, 31-60, 61-90) to be dynamic. it means these values should come from a table(as these are set up by user). user can set as many values as they want for getting result. How can I do that?

Answer 1

Assuming you have a second table like:

ASSIST_TABLE
FromAge|ToAge|Text
0|30|'0-30'

The you could do something like this.

 SELECT
 COUNT(id),
 FROM
 (
 select
   id,
   ISNULL(select text from ASSIST_TABLE
     where Age between FromAge andToAge),'NO CATEGORY') AS AGERANGE
from queue 
where DATE between '01-Apr-2011' and '05-May-2011'
 ) T
GROUP BY
AgeRange;

If you want to stick to your case-statement, you would have to make the statement dynamic. Which means generate first the query, store it into a variable and execute it at last. That is more work!

Answer 2

Here is another try: Dynamic SQL, it's not the finished answer, but you get the idea of it.

CREATE PROCEDURE sp_generate_valid_choices (IN p_request_id Bigint)
BEGIN
 DECLARE num_rows INT DEFAULT 0;
 DECLARE no_more_rows BINARY;
 DECLARE no_more_subrows BINARY;
 DECLARE loop_cntr INT DEFAULT 0;
 DECLARE var_choice_group BIGINT DEFAULT 0;

 -- Declare Cursor for the loop through the constraint_groups
 DECLARE cur_constraint_group CURSOR FOR
 SELECT distinct choice_constraint_group FROM aip_choice_constraint
    WHERE choice_id_rule_parameter IN (SELECT choice_id FROM aip_request_detail
                                        where request_id = p_request_id);
 -- DECLARE 'handlers' for exceptions
 DECLARE CONTINUE HANDLER FOR NOT FOUND
 SET no_more_rows := TRUE;

-- OPEN CURSOR AN PROCESS CONSTRAINT_GROUPS
OPEN cur_constraint_group;
SELECT FOUND_ROWS() INTO num_rows;

choice_group_loop: LOOP
    FETCH cur_constraint_group
    INTO var_choice_group;

IF no_more_rows THEN
    CLOSE cur_constraint_group;
    LEAVE choice_group_loop;
END IF;
-- PAYLOAD
-- INSERT THE VALID CHOCIES INTO tmp_aip_valid_choices 
 SELECT @var_sql_query := CONCAT('INSERT INTO tmp_aip_valid_choices ','SELECT ',p_request_id,' as request_id,  `aip_choice_constraint`.`choice_constraint_id`,`aip_choice_constraint`.`choice_constraint_group`
    ,AVG(IF (`aip_request_detail`.`choice_varchar_value`', `aip_choice_constraint`.`choice_constraint_operator`, '\'',`aip_choice_constraint`.`choice_constraint_value`, '\'',',1,0 )) AS VALID
FROM `aip_choice_constraint`
LEFT JOIN `aip_request_detail` ON `aip_request_detail`.`choice_id` = `aip_choice_constraint`.`choice_id_rule_parameter`
WHERE `aip_choice_constraint`.choice_constraint_group =' , var_choice_group,
' GROUP BY `aip_choice_constraint`.choice_constraint_group')
FROM `aip_choice_constraint` WHERE `aip_choice_constraint`.choice_constraint_group = var_choice_group;
PREPARE SQL_STATEMENT FROM @var_sql_query;
EXECUTE SQL_STATEMENT;
-- INCREMENT THE COUNTER
SET loop_cntr = loop_cntr + 1;

END LOOP choice_group_loop;

INSERT INTO tmp_aip_valid_choices_for_request
(request_id, choice_id)
SELECT DISTINCT p_request_id, choice_id FROM aip_choice ac
-- RULE 1 ALL CHOICES WITHOUT CONSTRAINTS
WHERE ac.choice_id NOT IN (SELECT choice_id_rule_target FROM aip_choice_constraint)
-- RULE 2 ALL CHOICES WITH CONSTRAINTS, THAT ARE NOT YET ANSWERED
OR ac.choice_id NOT IN (SELECT choice_id_rule_target FROM aip_choice_constraint
WHERE choice_id_rule_parameter IN (SELECT choice_id FROM aip_request_detail WHERE request_id = p_request_id))
-- RULE 3 ALL CHOICES WITH CONSTRAINTS, THAT ARE TRUE
OR ac.choice_id IN (SELECT choice_id_rule_target FROM aip_choice_constraint
WHERE choice_constraint_group IN (SELECT choice_constraint_group FROM tmp_aip_valid_choices WHERE request_id = p_request_id AND VALID = 1));

END //
Delimiter ;

The code is for MySQL, so you cannot copy it. But the idea is the same. Prepare your statement as string and then execute it.