MySQL not using the correct index












0















I have following readings table, it has around 500 million rows.



CREATE TABLE readings (
id int(11) NOT NULL AUTO_INCREMENT,
value double NOT NULL,
created_dt datetime NOT NULL,
device_id int(11) NOT NULL,
PRIMARY KEY (id),
UNIQUE KEY readings_created_dt_483d31a3654ede43_uniq (created_dt,device_id),
KEY readings_device_id_6a03c4ab761154d1_fk_device_id (device_id),
CONSTRAINT readings_device_id_6a03c4ab761154d1_fk_device_id FOREIGN KEY (device_id) REFERENCES device (id)
) ENGINE=InnoDB AUTO_INCREMENT=138611438 DEFAULT CHARSET=latin1


It has an index on (created_dt, device_id) and an index on device_id( which is foreign key)



When i run following query



SELECT value, created_dt FROM readings WHERE (created_dt BETWEEN '2019-03-17 19:11:00' AND '2019-03-18 19:11:00' AND (device_id) IN (10, 11, 12));


Above query takes around 2 minutes.



DESCRIBE query returns the index used is 'readings_device_id_6a03c4ab761154d1_fk_device_id' which is foreign key index on device_id. However if i remove the above index and run the query again, it uses 'readings_created_dt_483d31a3654ede43_uniq' which is an index on both (created_dt, device_id) and retuns data in less than a second.









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    0















    I have following readings table, it has around 500 million rows.



    CREATE TABLE readings (
    id int(11) NOT NULL AUTO_INCREMENT,
    value double NOT NULL,
    created_dt datetime NOT NULL,
    device_id int(11) NOT NULL,
    PRIMARY KEY (id),
    UNIQUE KEY readings_created_dt_483d31a3654ede43_uniq (created_dt,device_id),
    KEY readings_device_id_6a03c4ab761154d1_fk_device_id (device_id),
    CONSTRAINT readings_device_id_6a03c4ab761154d1_fk_device_id FOREIGN KEY (device_id) REFERENCES device (id)
    ) ENGINE=InnoDB AUTO_INCREMENT=138611438 DEFAULT CHARSET=latin1


    It has an index on (created_dt, device_id) and an index on device_id( which is foreign key)



    When i run following query



    SELECT value, created_dt FROM readings WHERE (created_dt BETWEEN '2019-03-17 19:11:00' AND '2019-03-18 19:11:00' AND (device_id) IN (10, 11, 12));


    Above query takes around 2 minutes.



    DESCRIBE query returns the index used is 'readings_device_id_6a03c4ab761154d1_fk_device_id' which is foreign key index on device_id. However if i remove the above index and run the query again, it uses 'readings_created_dt_483d31a3654ede43_uniq' which is an index on both (created_dt, device_id) and retuns data in less than a second.









    share







    New contributor




    Andro is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.























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      I have following readings table, it has around 500 million rows.



      CREATE TABLE readings (
      id int(11) NOT NULL AUTO_INCREMENT,
      value double NOT NULL,
      created_dt datetime NOT NULL,
      device_id int(11) NOT NULL,
      PRIMARY KEY (id),
      UNIQUE KEY readings_created_dt_483d31a3654ede43_uniq (created_dt,device_id),
      KEY readings_device_id_6a03c4ab761154d1_fk_device_id (device_id),
      CONSTRAINT readings_device_id_6a03c4ab761154d1_fk_device_id FOREIGN KEY (device_id) REFERENCES device (id)
      ) ENGINE=InnoDB AUTO_INCREMENT=138611438 DEFAULT CHARSET=latin1


      It has an index on (created_dt, device_id) and an index on device_id( which is foreign key)



      When i run following query



      SELECT value, created_dt FROM readings WHERE (created_dt BETWEEN '2019-03-17 19:11:00' AND '2019-03-18 19:11:00' AND (device_id) IN (10, 11, 12));


      Above query takes around 2 minutes.



      DESCRIBE query returns the index used is 'readings_device_id_6a03c4ab761154d1_fk_device_id' which is foreign key index on device_id. However if i remove the above index and run the query again, it uses 'readings_created_dt_483d31a3654ede43_uniq' which is an index on both (created_dt, device_id) and retuns data in less than a second.









      share







      New contributor




      Andro is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.












      I have following readings table, it has around 500 million rows.



      CREATE TABLE readings (
      id int(11) NOT NULL AUTO_INCREMENT,
      value double NOT NULL,
      created_dt datetime NOT NULL,
      device_id int(11) NOT NULL,
      PRIMARY KEY (id),
      UNIQUE KEY readings_created_dt_483d31a3654ede43_uniq (created_dt,device_id),
      KEY readings_device_id_6a03c4ab761154d1_fk_device_id (device_id),
      CONSTRAINT readings_device_id_6a03c4ab761154d1_fk_device_id FOREIGN KEY (device_id) REFERENCES device (id)
      ) ENGINE=InnoDB AUTO_INCREMENT=138611438 DEFAULT CHARSET=latin1


      It has an index on (created_dt, device_id) and an index on device_id( which is foreign key)



      When i run following query



      SELECT value, created_dt FROM readings WHERE (created_dt BETWEEN '2019-03-17 19:11:00' AND '2019-03-18 19:11:00' AND (device_id) IN (10, 11, 12));


      Above query takes around 2 minutes.



      DESCRIBE query returns the index used is 'readings_device_id_6a03c4ab761154d1_fk_device_id' which is foreign key index on device_id. However if i remove the above index and run the query again, it uses 'readings_created_dt_483d31a3654ede43_uniq' which is an index on both (created_dt, device_id) and retuns data in less than a second.







      mysql





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      Andro is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      asked 8 mins ago









      AndroAndro

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