Select columns from table1 join table2, taking very long time - mysql

Question

I have 2 tables. From these two tables i am trying to insert records into a third table using a select query with join. However i found that select query with join not using indexes and taking a lots of time, hence insertion is very slow.
I tried to create multiple indexes as suggested in few posts but not avail.
MySQL with JOIN not using index
MySQL query with JOIN not using INDEX
Here are my tables structure:
CREATE TABLE master_table (
id BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
field1 VARCHAR(50) DEFAULT NULL,
field2 VARCHAR(50) DEFAULT NULL,
field3 VARCHAR(50) DEFAULT NULL,
field4 VARCHAR(50) DEFAULT NULL,
PRIMARY KEY (id),
KEY mt_field1_index (field1)
) ENGINE=INNODB DEFAULT CHARSET=utf8;
CREATE TABLE child_table (
c_id BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
m_id BIGINT(20) UNSIGNED NOT NULL ,
group_id BIGINT(20) UNSIGNED NOT NULL ,
status ENUM('Status1','Status2','Status3') NOT NULL,
job_id VARCHAR(50) DEFAULT NULL,
PRIMARY KEY (c_id),
UNIQUE KEY ct_mid_gid (m_id,group_id),
KEY Index_ct_status (status),
KEY index_ct_jobid (job_id),
KEY index_ct_mid (m_id),
KEY index_ct_cid_sts_tsk (group_id,status,job_id)
) ENGINE=INNODB DEFAULT CHARSET=utf8;
Query:
SELECT m.id
, NULLIF(TRIM(m.field1),'')
FROM master_table m
JOIN child_table c
ON m.id = c.m_id
WHERE c.group_id = 2
AND c.status = 'Status3'
AND c.job_id = 0
ORDER
BY m.id
LIMIT 0, 1000;
Explain:
+-------+-------------+-------+------------+----------+------------------------------------------------------------------------------+-----------------+---------+--------------+-------+----------+------------------------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+-------+-------------+-------+------------+----------+------------------------------------------------------------------------------+-----------------+---------+--------------+-------+----------+------------------------------------------------+
| 1 | SIMPLE | c | (NULL) | ref | ct_mid_gid,Index_ct_status,index_ct_jobid,index_ct_mid,index_ct_cid_sts_tsk | Index_ct_status | 1 | const | 65689 | 0.00 | Using where; Using temporary; Using filesort |
| 1 | SIMPLE | m | (NULL) | eq_ref | PRIMARY | PRIMARY | 8 | r_n_d.c.m_id | 1 | 100.00 | (NULL) |
+-------+-------------+-------+------------+----------+------------------------------------------------------------------------------+-----------------+---------+--------------+-------+----------+------------------------------------------------+

Answer 1

WHERE c.group_id = 2
AND c.status = 'Status3'
AND c.job_id = 0
ORDER BY c.m_id -- Note the change
Needs
INDEX(group_id, status, job_id, -- in any order
m_id) -- last
What you have (separate indexes) is not the same.
In order to get to the LIMIT the index must get entirely past the WHERE and ORDER BY. This prevents computing all the rows (before the LIMIT) and sorting and only then do the LIMIT.
So, you get 4 speedups:
Index efficiently fetching the desired rows (from c)
No need for a sort pass (since ORDER BY delivers them in order)
The index is "covering" (hence, no bouncing back and forth between index BTree and data BTree for c)
Get to stop at 1000.
While you are at it, consider getting rid of the AUTO_INCREMENT. Toss c_id and change
PRIMARY KEY (c_id),
UNIQUE KEY ct_mid_gid (m_id, group_id)
-->
PRIMARY KEY(m_id, group_id)
Coincidentally, if you had done this, your KEY index_ct_cid_sts_tsk (group_id,status,job_id) would have stumbled into the perfect index. This is because the PK is implicitly tacked onto any secondary index, but you need m_id, not c_id. Anyway, I prefer to be explicit.
And when making changes, toss any redundant indexes. For example, KEY index_ct_mid (m_id) is useless since it is the beginning of another index.

Answer 2

Have you created index on the columns used in where clause?
Check query by adding index on columns.
but do remember if you add index then insert, update and delete operation on table might get slow.