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mysqlcodeigniterwhere-infind-in-set

difference between where_in and find_in_set

I am working on a join query in which I have to get the data from a column which contain the comma separated values.like allowed_activity contain 1,2,3,4,5,6 this the activity_id which is allowed.

So In the query, I am checking that current activity is allowed or not and for that, I have used where_in and also tried find_in_set in where condition.

Here is that part of the query:

$this->db->where_in('a.allowed_activity',$activity_id);
//And With FIND_IN_SET
$this->db->where("FIND_IN_SET($activity_id, a.allowed_activity) !=",0);

Problem or Confusion

When I use where_in it doesn't give me the result. But if I use FIND_IN_SET then it will return the desired result. I thought that where_in can do the task but it didn't.

Just Want to know why find_in_set working differently than where_in Because of both the function work same as finding the data is in comma separated list.

Here is the complete query:

SELECT mycolumns
FROM `table1` as `ea`
LEFT OUTER JOIN `table2` as `a` ON `ea`.`package_id` = `a`.`id`
LEFT OUTER JOIN `table3` as `e` ON `ea`.`employer_id` = `e`.`id`
WHERE `ea`.`card_id` > 0
AND FIND_IN_SET(6, a.allowed_activity) !=0
AND `ea`.`id` = '6'
ORDER BY `ea`.`creation_date` DESC

I am using Codeigniter Active record.

Solution

  • WHERE IN requires the set of values to be specified literally in the query, not as a single value containing a comma-delimited string. If you write:

    WHERE 6 IN (a.allowed_activity)

    it will treat a.allowed_activity as just a single value, and compare it with 6, not as a set of multiple values to search.

    FIND_IN_SET searches a comma-delimited string for the value.

    Another way to view it is that IN is a shortcut for a bunch of = tests combined with OR:

    WHERE x IN (a, b, c, d)

    is short for

    WHERE x = a OR x = b OR x = c OR x = d

    When you rewrite it like this, you can see clearly why it won't work with a column containing a comma-delimited string. It simply translates 

    WHERE 6 IN (a.allowed_activity)

    to:

    WHERE 6 = a.allowed_activity