Hi,
You could use JSON_TABLE() <https://mariadb.com/kb/en/json_table/> if
you store the values as JSON. The nice thing about JSON is that MariaDB
already has a lot of functions to work with it.
The syntax for converting each list in a row into its own row is IMO a
bit tricky to get right the first time but it seems to work. Here's an
example that I tested it with:
CREATE TABLE main_table(id INT PRIMARY KEY NOT NULL, to_join INT NOT NULL);
CREATE TABLE joined_table(id INT PRIMARY KEY NOT NULL, int_join JSON NOT
NULL);
INSERT INTO main_table VALUES (1, 1), (2, 2), (3, 3), (4, 4), (5, 5);
INSERT INTO joined_table VALUES (123, '[2,4]'), (456, '[3,5]'), (789,
'[1, 5, 3]');
-- This one splits the join table's values into individual rows
SELECT jt.*, js_t.*
FROM joined_table AS jt
CROSS JOIN JSON_TABLE(
jt.int_join, '$[*]' COLUMNS(
id INT PATH '$'
)
) js_t;
-- This one joins it to the main table
SELECT mt.id AS main_table_id, jt.id AS joined_table_id, js_t.id AS
joined_on
FROM joined_table AS jt
CROSS JOIN JSON_TABLE(
jt.int_join, '$[*]' COLUMNS(
id INT PATH '$'
)
) js_t
JOIN main_table mt ON (js_t.id = mt.to_join)
ORDER BY jt.id;
The SQLFiddle for it can be found here:
https://sqlfiddle.com/mariadb/online-compiler?id=5f6d5772-815f-48a4-977c-9903a00d683c
Markus Mäkelä
On 9/13/24 17:09, Gingko via discuss wrote:
Hello,
I would like to know if is there some (efficient!) way to join two
tables on a list of values
contained in (likely a single column) of the joined table, whatever
form could have
this list of values ?
For example, I have a main table containing:
main_table:
+------------+------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+------------------+------+-----+------------+----------------+
| index | int(11) | NO | PRI | 0 | |
| to_join | int(11) | NO | | 0 | |
| <other fields, irrelevant> | | | | |
+------------+------------------+------+-----+------------+----------------+
… and a secondary table containing:
joined_table:
+------------+------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default |
Extra |
+------------+------------------+------+-----+------------+----------------+
| index | int(11) | NO | PRI | |
auto_increment |
| int_list | <list_of_ints> | YES | | (empty)
| |
| <other fields, irrelevant> | | | |
|
+------------+------------------+------+-----+------------+----------------+
We could suppose, here, as a simple test case, that main_table has
five rows
where to_join contains respectively 1, 2, 3, 4, and 5,
and the joined_table has a single row with the single column int_list
combining 2 and 4
in any form (but of course, this list could actually have any length).
I'd like to join these tables using a statement like:
SELECT
<anything>
FROM main_table AS M
LEFT JOIN joined_table AS J
ON M.to_join <some_operator to> J.int_list;
… in such a way that main_table would be joined to joined_table using
any value
contained in int_list, and the statement is expected to give two rows
as a result.
I tried to set int_list as a TINYTEXT containing "2,4" and use:
SELECT
<anything>
FROM main_table AS M
LEFT JOIN joined_table AS J
ON M.to_join IN (J.int_list);
… but this doesn't work, of course, my comma separated list is seen as
a whole single value.
I also tried, still using TINYTEXT, the list as "[2][4]" and use:
SELECT
<anything>
FROM main_table AS M
LEFT JOIN joined_table AS J
ON J.int_listLIKE CONCAT('%[', M.to_join , ']%');
This works (more or less), but it is excruciatingly slow, especially
knowing that main_table
can actually contain millions of rows, and joined_table several thousands.
Is there a better solution for doing that?
As the final goal implies, somewhere later, associating to_join in
main_table, via int_list,
to the index auto increment primary key of the joined_table, using
multiple rows there
is not an option.
Regards,
Gingko
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Markus Mäkelä, Senior Software Engineer
MariaDB Corporation
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