Knex.js Getting values from comma-separated - sql

Question

I have two SQlite3 tables task and tags
task is my master table and tags is storing tag names
I store comma-separated values in task
Now I want to get Tag names with use of a knex.js
table task
id task tags
---------------------
1 abc 1,2,3
2 xyz 3,1
3 apple 2
table tags
id tag
------------
1 cold
2 hot
3 normal
Now i want output as below
OUTPUT:
id task tags
---------------------
1 abc cold,hot,normal
2 xyz normal,cold
3 apple hot
I know i will have to use joins but not sure how to actually use it in knex.js. Please do help me.

Answer 1

Part of the problem is that your database is not properly normalised. Instead of having two tables task and tabs, with table tasks containing multiple tag IDs in the column 'tags' you should have three tables; 'tasks', 'tags' and the 'joining' table 'task_tags'. They would store the following data...
Tasks
id task
----------
1 abc
2 xyz
3 apple
Tags
id tag
------------
1 cold
2 hot
3 normal
task_tags
task_id tag_id
1 1
1 2
1 3
2 1
2 3
3 2
Now you can have as many tags as you like (whether or not any tasks use them) and as many tasks as you like (whether or not they use any tags) and you associate a task with it's tags via the task_tags table.
Then to get the result you want you would use the select
SELECT
tasks.id,
tasks.task,
GROUP_CONCAT(tags.tag) -- this gives you the csv line eg cold,hot,normal
from tasks
left join task_tags
ON tasks.id = task_tags.task_id
left join tags
on tags.id = task_tags.tag_id
GROUP BY task.id, tags.id
see https://www.sqlite.org/lang_aggfunc.html for explanation of GROUP_CONCAT

Answer 2

Your task table should be redesigned to hold one tag per row, not multiple tags in a single row:
id task tag
---------- ---------- ----------
1 abc 1
1 abc 2
1 abc 3
2 xyz 3
2 xyz 1
3 apple 2
Then it's easy:
SELECT task.id, task.task, group_concat(tags.tag, ',') AS tags
FROM task
JOIN tags ON task.tag = tags.id
GROUP BY task.id, task.task
ORDER BY task.id;
which gives
id task tags
---------- ---------- ---------------
1 abc cold,hot,normal
2 xyz normal,cold
3 apple hot
A design that follows the rules of relational databases makes life much easier (And the above can be normalized further; see the other answer); while some databases do support array types, sqlite is not one of them. If you insist on keeping your current design, though, there's an ugly hack involving the JSON1 extension and turning your CSV list of numbers into a JSON array:
SELECT task.id, task.task, group_concat(tags.tag, ',') AS tags
FROM task
JOIN json_each('[' || task.tags || ']') AS j
JOIN tags ON tags.id = j.value
GROUP BY task.id, task.task
ORDER BY task.id;