Mysql: insert multiple values with order number - mysql

Question

I want to split a string like ('abc', 'dev', dfg') and insert into a table with its order number like that:
index value
1 abc
2 dev
3 dfg
Is anyway I can do this in mysql? The size is unknown.

Answer 1

You probably can do something like this:
WITH RECURSIVE cte AS (
SELECT 1 idx, LENGTH(REGEXP_REPLACE(stringVal,'[^,]',''))+1 AS maxLen
FROM mytable UNION
SELECT idx+1, maxLen FROM cte WHERE idx+1 <= maxLen)
SELECT idx,
SUBSTRING_INDEX(SUBSTRING_INDEX(stringVal,',',idx),',',-1) AS val
FROM cte
CROSS JOIN mytable;
Generating idx using cte based on how many strings were separated by comma in the column. The steps are:
Use REGEXP_REPLACE() to replace any value that is not comma; returns ,,.
Use LENGTH() on the regexp to get the total of comma; returns 2.
Add 1 (+1) to the length result returned; final value 3.
The cte result are:
+-----+--------+
| idx | maxLen |
+-----+--------+
| 1 | 3 |
| 2 | 3 |
| 3 | 3 |
+-----+--------+
From the generated cte , we're going to use idx value with SUBSTRING_INDEX() to separate the comma-separated, single-row string into multiple rows.
Understanding what the query is doing:
This, we can emulate with 3 of the same query repeated UNION ALL together like the following:
SELECT 1 AS 'index',
SUBSTRING_INDEX(SUBSTRING_INDEX(stringVal,',',1),',',-1) AS val
FROM mytable
UNION ALL
SELECT 2,
SUBSTRING_INDEX(SUBSTRING_INDEX(stringVal,',',2),',',-1)
FROM mytable
UNION ALL
SELECT 3,
SUBSTRING_INDEX(SUBSTRING_INDEX(stringVal,',',3),',',-1)
FROM mytable;
Which also can be done as such; Same idea as the cte approach:
SELECT idx,
SUBSTRING_INDEX(SUBSTRING_INDEX(stringVal,',',idx),',',-1) AS val
FROM (SELECT 1 idx UNION
SELECT 2 UNION
SELECT 3 ) i
CROSS JOIN mytable;
Both of these query return the same result as the cte approach however it's not an ideal one; since we have to manually check how many string separated by comma and define (hard-code) it in the query. Imagine if a single row of string consists of something like a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z - all the 26 alphabet; then that means the UNION query need to be repeated 26 times.
Demo fiddle