Mysql: Split (explode) comma delimited column values to rows

Description
Following is Table Structure:
eligibility_table

ID     COURSE_ID     BRANCH_IDS
1      501           621,622,623
1      502
1      503           625
2      501           621
2      505           650
3      500

Now, I am making new table structure as describe below and inserting course_table,branch_table through eligibility_table. So following, final output I want
course_table

ID COURSE_ID
1  501
1  502
1  503
2  501
2  505
3  500

branch_table

ID BRANCH_ID
1  621
1  622
1  623
1  625
2  621
2  650

Solution: 

INSERT INTO branch_table (id, branch_id)
SELECT e.id, SUBSTRING_INDEX(SUBSTRING_INDEX(e.branch_ids, ',', n.n), ',', -1) branch_id
  FROM eligibility_table e CROSS JOIN 
(
   SELECT a.N + b.N * 10 + 1 n
     FROM 
    (SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
   ,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
    ORDER BY n
) n
 WHERE n.n <= 1 + (LENGTH(e.branch_ids) - LENGTH(REPLACE(e.branch_ids, ',', '')))
 ORDER BY id, branch_id

• The subquery with an alias of n generates on the fly a sequence of numbers (numbers or tally table) from 1 to 100 in this particular case using UNION ALL and CROSS JOIN. Sometimes it's handy to have a real tally table in your db.
• In outer select innermost SUBSTRING_INDEX() gets everything up to n'th element in a list and outer SUBSTRING_INDEX() extract right most part after a last delimiter effectively getting n-th element itself.
• CROSS JOIN allows us to produce a set of rows which is a cartesian product (of 100 rows in n and all rows in eligibility_table)
• condition in WHERE clause filters out all unnecessary rows from the resultset

Note: this query will split up to 100 branch ids. If you need more or less you can adjust a limit by editing the inner subquery
Result in branch_table:
| ID | BRANCH_ID |
------------------
| 1 | 621 |
 | 1 | 622 |
 | 1 | 623 |
 | 1 | 625 |
 | 2 | 621 |
 | 2 | 650 |