Mysql stored procedure if count is never null - mysql

Question

I got a table that is being updated every 5 Minutes by a Script Call, triggered by a http request. The table looks like this
MariaDB > select host_id, ping_eu, disk_usage,insert_time from sequencial_host;
+---------+---------+-------------+---------------------+
| host_id | ping | disk_usage | insert_time |
+---------+---------+-------------+---------------------+
| 1 | 35.60 | 10329416704 | 2016-01-20 20:47:51 |
| 2 | 36.57 | 2902848512 | 2016-01-20 20:48:06 |
+---------+---------+-------------+---------------------+
I want to prevent a mess in case the script runs amok or any malicious intent by calling a stored procedure that allows inserting if the last insert_time was at least 4,5 Minutes ago. (30 second script built in time out, so more a less accurate).
I built this Procedure:
CREATE PROCEDURE `update_table`(
IN host_id_a int(11),
IN insert_time timestamp,
IN disk_usage bigint(20) ,
IN ping decimal(10,2)
BEGIN
DECLARE count INT;
SELECT count(insert_time) INTO count FROM db.sequencial_host WHERE insert_time > (NOW() - INTERVAL 270 SECOND) AND host_id = host_id_a ORDER BY insert_time DESC LIMIT 1;
IF count < 1 THEN
INSERT INTO db.sequencial_host ( `host_id`,`insert_time`,`disk_usage`,`ping`)
VALUES( host_id_a, CURRENT_TIMESTAMP, disk_usage, ping);
END IF;
END
If I leave away the If clause, the Insert Statements work by calling the procedure and the Select Query also works for itself if executed in the shell.
I am using MariaDB 5.5.46-1ubuntu0.14.04.2.
I nearly tried any combination of IF count = 0, IF count IS NULL, IF (SELECT ..) IS NULL.
Could anybody take look?
With kind regards Joey
EDIT:
MariaDB [tempdb]> SELECT count(*) FROM tempdb.sequencial_host WHERE insert_time > (NOW() - INTERVAL 270 SECOND) AND host_id = 1 ORDER BY insert_time DESC LIMIT 1;
+--------------------+
| count(insert_time) |
+--------------------+
| 0 |
+--------------------+
1 row in set (0.01 sec)
MariaDB [tempdb]> SELECT count(*) FROM tempdb.sequencial_host WHERE insert_time > (NOW() - INTERVAL 2 HOUR) AND host_id = 1 ORDER BY insert_time DESC LIMIT 1;
+--------------------+
| count(insert_time) |
+--------------------+
| 1 |
+--------------------+
Edit 2:
Pastebin containing all relevant database information in complete. pastebin.com/99eEDLy4
Edit 3:
If I change it to cnt = 1 I can spam the query and it fills everything, but only if there is data in the table. With a freshly truncated one I need to set it to 0 to get values in there.

Answer 1

count cant never < 0 . count is everytime a positive number between 0 and n. So
IF count < 0 THEN
never works
change it to
IF count > 0 THEN

Answer 2

Count on a column that is or has null, will only return count of those values which are not null. If all column values are null then null is returned.
In this case your where clause is ensuring no records return thus all column values for insert_Time will be null; thus null is returned. However, if you had multiple records without null insert_time; then the count would represent those records without a null insert_time.
I think you want count(*) instead of count(insert_time) to ensure 0 is returned when no records are found.
CREATE PROCEDURE `update_table`(
IN host_id_a int(11),
IN insert_time timestamp,
IN disk_usage bigint(20) ,
IN ping decimal(10,2))
BEGIN
DECLARE count INT;
SELECT count(*) INTO count FROM db.sequencial_host WHERE insert_time > (NOW() - INTERVAL 270 SECOND) AND host_id = host_id_a ORDER BY insert_time DESC LIMIT 1;
IF count < 1 THEN
INSERT INTO db.sequencial_host ( `host_id`,`insert_time`,`disk_usage`,`ping`)
VALUES( host_id_a, CURRENT_TIMESTAMP, disk_usage, ping);
END IF;
END

Answer 3

It's not a bug, it's a feature.
Inside of a Stored Procedure Select Exists returns 1 when there is data in the table and null if there is no, when the query is written like that (without specific table set in the where clause):
SELECT EXISTS (SELECT * INTO count FROM db.sequencial_host WHERE insert_time > (NOW() - INTERVAL 270 SECOND) AND host_id = host_id_a ORDER BY insert_time DESC LIMIT 1);
If you append the table to the host id it works as expected. Even counts return the expected value. SELECT EXISTS (SELECT * INTO count FROM db.sequencial_host WHERE insert_time > (NOW() - INTERVAL 270 SECOND) AND sequencial_host.host_id = host_id_a ORDER BY insert_time DESC LIMIT 1);