Parse in MySQL using comma as delimiter - mysql

Question

I have two tables
Table1 with list of users comma separated
Name UserID
abc A,B,C,D
def A,B,C
Table2
Name UserID
abc A
abc B
abc C
def A
def B
I need to find the users that are in table1 for each Name but not in table2 (There won't ever be an instance when a UserID to Name pair is present in table2 but not in table1 as CSV).
The output should be
Name UserID
abc D
def C
I can do this with PHP but is there a way this can be done through a query? I am not sure where to begin in case I'm doing this as a query. Can I parse in MySQL using comma as delimiter?

Answer 1

I plugged your test data into a test schema in SQLFiddle and ran the query that follows.
Here's the link to SQLFiddle with the test and positive results:
http://sqlfiddle.com/#!2/83dfd/4/0
Here's the query:
SELECT
COALESCE(NORMALIZED_TABLE1.NAME, TABLE2.NAME) AS NAME,
COALESCE(NORMALIZED_TABLE1.USERID, TABLE2.USERID) AS USERID
FROM (
SELECT NAME,
SUBSTRING(
USERID
FROM CASE
WHEN INDEX_TABLE.POS = 1 THEN 1
ELSE INDEX_TABLE.POS + 1
END
FOR CASE LOCATE(',', USERID, INDEX_TABLE.POS + 1)
WHEN 0 THEN CHARACTER_LENGTH(USERID) + 1
ELSE LOCATE(',', USERID, INDEX_TABLE.POS + 1)
END
- CASE
WHEN INDEX_TABLE.POS = 1 THEN 1
ELSE INDEX_TABLE.POS + 1
END
) AS USERID
FROM TABLE1
INNER JOIN (
SELECT #rownum:=#rownum+1 POS
FROM (
SELECT 0 UNION SELECT 1 UNION SELECT 2 UNION SELECT 3
UNION SELECT 4 UNION SELECT 5 UNION SELECT 6
UNION SELECT 7 UNION SELECT 8 UNION SELECT 9
) a, (
SELECT 0 UNION SELECT 1 UNION SELECT 2 UNION SELECT 3
UNION SELECT 4 UNION SELECT 5 UNION SELECT 6
UNION SELECT 7 UNION SELECT 8 UNION SELECT 9
) b, (
SELECT 0 UNION SELECT 1 UNION SELECT 2 UNION SELECT 3
UNION SELECT 4 UNION SELECT 5 UNION SELECT 6
UNION SELECT 7 UNION SELECT 8 UNION SELECT 9
) c, (SELECT #rownum:=0) r
) INDEX_TABLE
ON INDEX_TABLE.POS <= CHAR_LENGTH(TABLE1.USERID)
AND (
INDEX_TABLE.POS = 1
OR SUBSTRING(USERID FROM INDEX_TABLE.POS FOR 1) = ','
)
) AS NORMALIZED_TABLE1
LEFT OUTER JOIN TABLE2
ON NORMALIZED_TABLE1.NAME = TABLE2.NAME
AND NORMALIZED_TABLE1.USERID = TABLE2.USERID
WHERE TABLE2.NAME IS NULL;
If you have very long column width in table1 you might need to expand the "INDEX_TABLE" subquery. You can copy and paste over it with the code at this link to do so:
http://www.experts-exchange.com/Database/MySQL/A_3573-A-MySQL-Tidbit-Quick-Numbers-Table-Generation.html

Answer 2

If you table is fixed (you are wanted to work on those tables) then design a class to read data from them instead of directly saving the set data from those predefined tables; let your object to process the read data live across your application domain to get a full-blown accessibility. :-D