select * from t limit #var - mysql

Question

I am using multi-value option on grafana to select metrics and display them dynamically, this method works on graphs fine because I am not putting any limiter but I want to use Gauge to display the last entered data and the selected options to show the desired metric like this
.
And here i am stuck.
here is things i tried but naah didn't work,;
I tried to create a procedure for test;
CREATE PROCEDURE getData()
BEGIN
SET #itemlimit := JSON_LENGTH(JSON_ARRAY('conductivite0','conductivite1'));
SELECT UNIX_TIMESTAMP(datetime) as time_sec,
value as value,
label as metric
FROM valeur_capteur_SD
WHERE label in ('conductivite0','conductivite1')
ORDER BY id DESC LIMIT 0, #itemlimit;
END //
DELIMITER ;
and using a variable,
SET #var =
(
SELECT vars
FROM (
SELECT
JSON_LENGTH(
REPLACE(
CONCAT("[", "'conductivite0','conductivite1'", "]"),"'",'"'
)
) 'vars') as vars
);
SELECT
UNIX_TIMESTAMP(datetime) as time_sec,
value as value,
label as metric
FROM valeur_capteur_SD
WHERE label in ('conductivite0','conductivite1','debit0')
ORDER BY id DESC
LIMIT #var;

Answer 1

Well, after struggling for hours i found out a way to deal with it
DELIMITER //
CREATE PROCEDURE `getSelectedSensors`(IN param TEXT)
BEGIN
SET #query1 := CONCAT("
SELECT UNIX_TIMESTAMP(datetime) as time_sec,value as value, label as metric
FROM valeur_capteur_SD WHERE label in (",param,")
ORDER BY id DESC
LIMIT 0, ?");
PREPARE stmt1 FROM #query1;
SET #itemlimit = (LENGTH(param) - LENGTH(REPLACE(param, ',', ''))) +1;
EXECUTE stmt1 USING #itemlimit;
DEALLOCATE PREPARE stmt1;
END;