FIND_IN_SET() vs IN()

Question

I have 2 tables in my database. One is for orders, and one is for companies.

Orders has this structure:

OrderID     |     attachedCompanyIDs
-------         


        

Answer 1

because the second query is looking for rows with the id's 1 OR 2 OR 3, the first query is looking for a one of the comma delimited values to exist in companyID,

and another problem here is you aren't joining the tables on a common key in your where so you are going to get a mutation of rows that = count(table1) * count(table2);

Your problem really exists with part 2 of my answer. (with your second query)

Answer 2

SELECT o.*, GROUP_CONCAT(c.name) FROM Orders AS o , Company.c
    WHERE FIND_IN_SET(c.CompanyID , o.attachedCompanyIDs) GROUP BY o.attachedCompanyIDs

Answer 3

attachedCompanyIDs is one big string, so mysql try to find company in this its cast to integer

when you use where in

so if comapnyid = 1 :

companyID IN ('1,2,3')

this is return true

but if the number 1 is not in the first place

 companyID IN ('2,3,1')

its return false

Answer 4

To get the all related companies name, not based on particular Id.

SELECT 
    (SELECT GROUP_CONCAT(cmp.cmpny_name) 
    FROM company cmp 
    WHERE FIND_IN_SET(cmp.CompanyID, odr.attachedCompanyIDs)
    ) AS COMPANIES
FROM orders odr

Answer 5

SELECT  name
FROM    orders,company
WHERE   orderID = 1
        AND companyID IN (attachedCompanyIDs)

attachedCompanyIDs is a scalar value which is cast into INT (type of companyID).

The cast only returns numbers up to the first non-digit (a comma in your case).

Thus,

companyID IN ('1,2,3') ≡ companyID IN (CAST('1,2,3' AS INT)) ≡ companyID IN (1)

In PostgreSQL, you could cast the string into array (or store it as an array in the first place):

SELECT  name
FROM    orders
JOIN    company
ON      companyID = ANY (('{' | attachedCompanyIDs | '}')::INT[])
WHERE   orderID = 1

and this would even use an index on companyID.

Unfortunately, this does not work in MySQL since the latter does not support arrays.

You may find this article interesting (see #2):

• 10 things in MySQL (that won’t work as expected)

Update:

If there is some reasonable limit on the number of values in the comma separated lists (say, no more than 5), so you can try to use this query:

SELECT  name
FROM    orders
CROSS JOIN
        (
        SELECT  1 AS pos
        UNION ALL
        SELECT  2 AS pos
        UNION ALL
        SELECT  3 AS pos
        UNION ALL
        SELECT  4 AS pos
        UNION ALL
        SELECT  5 AS pos
        ) q
JOIN    company
ON      companyID = CAST(NULLIF(SUBSTRING_INDEX(attachedCompanyIDs, ',', -pos), SUBSTRING_INDEX(attachedCompanyIDs, ',', 1 - pos)) AS UNSIGNED)

Answer 6

Let me explain when to use FIND_IN_SET and When to use IN.

Let's take table A which has columns named "aid","aname". Let's take table B which has columns named "bid","bname","aids".

Now there are dummy values in Table A and Table B as below.

Table A

aid aname

1 Apple

2 Banana

3 Mango

Table B

bid bname aids

1 Apple 1,2

2 Banana 2,1

3 Mango 3,1,2

enter code here

Case1: if you want to get those records from table b which has 1 value present in aids columns then you have to use FIND_IN_SET.

Query: select * from A JOIN B ON FIND_IN_SET(A.aid,b.aids) where A.aid = 1 ;

Case2: if you want to get those records from table a which has 1 OR 2 OR 3 value present in aid columns then you have to use IN.

Query: select * from A JOIN B ON A.aid IN (b.aids);

Now here upto you that what you needs through mysql query.