difference between where_in and find_in_set

Question

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<

Answer 1

FIND_IN_SET search for a value in a array and return the index of the value then if the function is different than 0 this mean that the value in present in the list . so the code

  this->db->where("FIND_IN_SET(6, a.allowed_activity) !=",0);

mean return the index of the value 6 in a.allowed_activity
and if the value return is different that 0 then the value 6 is present in a.allowed_activity

WHERE ... IN check if the value in the set but don't return the index .. just return true or false if the value is present or not

Answer 2

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

Answer 3

The following code is incorrect:

$this->db->where("FIND_IN_SET($activity_id, a.allowed_activity) !=",0);

I'm surprised this even runs without error, but one possibility is that it is generating a WHERE clause which compares a string against 0. Of course, they will never be equal, and so this will always be true.

If you want to call the native FIND_IN_SET() function, then you would need to use whereRaw():

$this->db->whereRaw("FIND_IN_SET($activity_id, a.allowed_activity) !=0");

Using WHERE IN (...) is incorrect here, because you have all the values in a single row, separated from commas. WHERE IN would make sense if you wanted to filter for certain values from many rows, each column having a single value.