what is causing error (operands should contain 1 column) - mysql

Question

I am trying to set myItemId so that I can use it in the concat query. Everything works fine until I add this row
SET myItemID = (SELECT * FROM items i WHERE i.name LIKE '%KW PRE FREE COOLING%');
It then gives me an error of
Operand should contain 1 column(s)
Here is the query that I am working with
CREATE PROCEDURE reportFreeCoolingTempTable (
IN fromDate VARCHAR (50),
IN toDate VARCHAR (50),
IN timeZone VARCHAR (50)
)
BEGIN
DECLARE startDate VARCHAR (50);
DECLARE endDate VARCHAR (50);
DECLARE mylogID INT;
DECLARE myItemID int;
SET startDate = FROM_UNIXTIME(fromDate/1000);
SET endDate = FROM_UNIXTIME(toDate/1000);
SET mylogID = (SELECT logID FROM logs WHERE details LIKE 'FCT%' LIMIT 1);
SET myItemID = (SELECT * FROM items i WHERE i.name LIKE '%KW PRE FREE COOLING%');
SET #sql = NULL;
SET #sql = NULL;
SET #sql = CONCAT(
'SELECT #row:=#row+1 as rownum,
a.logid ,
L1.recordId,
L2.recordId as next_recordId,
L1.completed,
L2.completed as next_completed,
L1.activityId,
L2.activityId as next_activityId,
IF(L1.activityId = L2.activityId,1,NULL) as isError,
TIME_TO_SEC(TIMEDIFF(L2.completed, L1.completed)) / 3600 AS coolingHours,
((L1.item31985 - L1.item31987) * (time_to_sec(timediff(L2.completed, L1.completed)))) / 3600 AS kwDifference,
((L1.item31985 - L1.item31987) * (substr(l.details, instr(l.details , '':'' ) +1))) AS cost,
( (((L1.item31985 - L1.item31987) * (substr(l.details, instr(l.details , '':'' ) +1)))
*(time_to_sec(timediff(L2.completed, L1.completed)) / 3600))) AS costT,
time_to_sec(timediff(''', endDate, ''', ''', startDate, ''')) / 3600 AS totalTimeRange,
CONVERT_TZ(''', startDate, ''', ''UTC'', ''', timeZone, ''') AS startingDate,
CONVERT_TZ(''', endDate, ''', ''UTC'', ''', timeZone, ''') AS endingDate,
DATABASE() AS databaseName
FROM
(SELECT #row:=0)R,
(SELECT T1.completed,
(SELECT MIN(completed)
FROM log1644
WHERE completed > T1.completed) AS next_completed
FROM log',mylogID, ' T1
ORDER BY T1.completed
)TimeOrder
LEFT JOIN log', mylogID, ' L1 ON (L1.completed = TimeOrder.completed)
LEFT JOIN log', mylogID, ' L2 ON (L2.completed = TimeOrder.next_completed)
LEFT JOIN activities a ON L1.activityId = a.activityId
LEFT JOIN logs l ON a.logId = l.logId
Left Join items i ON l.logId = i.logId AND i.name LIKE ''%KW%''
WHERE i.itemID = 31985
AND L1.completed BETWEEN ''', startDate, ''' AND ''', endDate, '''
ORDER BY L1.completed');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END //
DELIMITER ;

Answer 1

Error itself explains (operands should contain 1 column) you need to select the single column from the query in order to set myItemID ,you are selecting all the columns from the items try this
SET myItemID = (SELECT id FROM items i WHERE i.name LIKE '%KW PRE FREE COOLING%' LIMIT 1 );
I assume the you need to set the myItemID to the id column from items where you conditions matches.i have also added LIMIT 1 in order to avoid the error of subquery should return one result

Answer 2

The error is caused because the SET statement expects a single value to be returned from your subquery. Not only can it return multiple values (SELECT *), but it can potentially return multiple rows. Change your query to specify just the single column from your subquery that you want to assign to myItemId, and ensure that it can return only 1 row - like this:
SET myItemID = (SELECT TOP 1 [itemIdColumnName] FROM items i WHERE i.name LIKE '%KW PRE FREE COOLING%');

Answer 3

The 'operand' in your case is "myItemID". It can only hold ONE value. Your SELECT statement returns all the rows in the table (multiple columns). You need to select only the 1 column that represents the ID you are trying to obtain.