Mysql Query taking long time where using variable - mysql

Question

I had an mysql event and runs eery day at 9:45 AM.
Begin
SET #v_ym :=(SELECT extract(year_month from DATE_SUB(SYSDATE(),INTERVAL 1 DAY)));
SELECT CAST(#ym AS CHAR);
select ssaname,extract(year_month from date_sub(sysdate(),interval 1 day)) ym,
omcr.btscount_ssa(ssaname) btscount,sum(case when duration>30 then duration else 0 end) dur_30 from
btsoutage.bts_faults
where ym=#v_ym and ssaname is not null
group by ssaname;
END;
in the query [ym is yearmonth and ym is indexed] when i substitute with variable #v_ym it is taking full table scan and the table is locked for further inserts. where as when i given the value directly it is using index and the output is fast.
The table contains more than 10 million records.
Create table is
CREATE TABLE `bts_faults` (
`bts_name` varchar(250) DEFAULT NULL,
`make` varchar(10) DEFAULT NULL,
`occuredtime` datetime DEFAULT NULL,
`clearedtime` datetime DEFAULT NULL,
`duration` int(10) DEFAULT NULL,
`reason` varchar(100) DEFAULT NULL,
`site_type` varchar(10) DEFAULT NULL,
`tech` varchar(5) DEFAULT NULL,
`fault_id` bigint(20) NOT NULL AUTO_INCREMENT,
`ssaname` varchar(20) DEFAULT NULL,
`fault_type` int(1) DEFAULT '0',
`remarks` varchar(250) DEFAULT NULL,
`bts_section` varchar(100) DEFAULT NULL,
`vendor` varchar(50) DEFAULT NULL,
`occureddate` date DEFAULT NULL,
`cleareddate` date DEFAULT NULL,
`ym` varchar(6) DEFAULT NULL,
`updatedate` datetime DEFAULT NULL,
`USERNAME` varchar(100) DEFAULT NULL,
`mask` int(1) DEFAULT '0',
`mask_cat` varchar(10) DEFAULT NULL,
`outage_cat` varchar(20) DEFAULT NULL,
`site_category` varchar(50) DEFAULT NULL,
`escalated_time` datetime DEFAULT NULL,
`zone` varchar(20) DEFAULT NULL,
`zone_fault_reason` varchar(500) DEFAULT NULL,
`zone_fault_remarks` varchar(500) DEFAULT NULL,
`zone_username` varchar(20) DEFAULT NULL,
`zone_updatetime` datetime DEFAULT NULL,
`zone_fault_duration` int(11) DEFAULT NULL,
`fault_category` varchar(250) DEFAULT NULL,
`remarks_1` varchar(2500) DEFAULT NULL,
PRIMARY KEY (`fault_id`),
UNIQUE KEY `UIDX_BTS_FAULTS` (`bts_name`,`occuredtime`),
KEY `indx_btsfaults_ym` (`ym`),
KEY `indx_btsfaults_cleareddate` (`cleareddate`),
KEY `Index_btsfaults_btsname` (`bts_name`),
KEY `index_btsfaults_ssaname` (`ssaname`),
KEY `indx_btsfaults_occureddate` (`occureddate`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=3807469710 DEFAULT CHARSET=latin1
The Explain Plan for the 2 type are

Answer 1

What percentage of the table is in the "current month"? If that is more than something like 20%, then there is no fix -- a table scan is likely to be faster. If it is less than 20%, then, as you suspect, #variables may be the villain. In that case, change the test to be
WHERE ym = CAST(
extract(year_month from DATE_SUB(SYSDATE(),INTERVAL 1 DAY))
AS CHAR)
AND ...
Much faster would be to build and maintain a Summary Table with a PRIMARY KEY of day and ssaname. This would have the subtotals for each day. It would be maintained either as the data is INSERTed or each night after midnight.
Then the 9:45 query becomes very fast. Maybe so fast that you don't even need to do it just once a day, but instead "on-demand".
More discussion: http://mysql.rjweb.org/doc.php/summarytables
I suggest you use NOW() instead of SYSDATE() -- The former is constant throughout a statement; the latter is not.
bts_faults looks like it might be a terabyte in size. If so, you probably don't want to here ways to make is smaller.
If the Auto_inc value is at 3.8B, yet there are only 10M rows, does this mean that you are purging 'old' data? Do you want to discuss speeding up the Deletes? (Start a new Question if you do.)