I have divided the SELECT query into segments and run them individually. The first two SELECT queries are the separate segments. The third SELECT query is the entire query without the line “ORDER BY measurment_is_delayed DESC , severity DESC”. – This is working. The last query is the full query that fails and gives us the same result in the mariadb.log as seen before. We tried to do the same thing in the earlier installation of the server, but here we also saw problems with the LEFT JOIN. This seems to have disappeared now. MariaDB [(none)]> use tcm_offline Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed MariaDB [tcm_offline]> SELECT -> SUBSTRING_INDEX(SUBSTRING_INDEX(MeasurementKey, '/', 2), '/', - 1) AS turbine, -> IFNULL(MAX(IF(AckStatus = 'UnAck', IF(ISNULL(ToTime), CASE -> WHEN -> AlarmType LIKE '%Red%' -> OR AlarmType LIKE 'Overrun' -> THEN -> 8 -> WHEN AlarmType LIKE '%Yellow%' THEN 7 -> WHEN AlarmType LIKE 'Blue%' THEN 6 -> ELSE 0 -> END, 2), IF(ISNULL(ToTime), CASE -> WHEN -> AlarmType LIKE '%Red%' -> OR AlarmType LIKE 'Overrun' -> THEN -> 5 -> WHEN AlarmType LIKE '%Yellow%' THEN 4 -> WHEN AlarmType LIKE 'Blue%' THEN 3 -> ELSE 0 -> END, 1))), - 1) AS severity -> FROM -> alarm_events -> WHERE -> site_index = 2 AND site_index IN (1 , 2) -> GROUP BY turbine; +--------------+----------+ | turbine | severity | +--------------+----------+ | MSYS_NACELLE | 8 | +--------------+----------+ 1 row in set (0.00 sec) MariaDB [tcm_offline]> SELECT -> site_index, -> turbine_id AS wt_id, -> turbine_serial AS wt_serial, -> turbine_name AS wt_turbine, -> display_name AS wt_name, -> (SELECT -> SUM(CASE -> WHEN -> (severity = 'fault' -> OR severity = 'emergency') -> AND acknowledged = 'no' -> AND syslog_events.state = 'active' -> THEN -> 1 -> ELSE 0 -> END) -> FROM -> syslog_events -> WHERE -> syslog_events.location_serial = turbine_serial) AS unack_syslogs, -> (SELECT -> SUM(CASE -> WHEN -> (severity = 'fault' -> OR severity = 'emergency') -> AND syslog_events.state = 'active' -> THEN -> 1 -> ELSE 0 -> END) -> FROM -> syslog_events -> WHERE -> syslog_events.location_serial = turbine_serial) AS syslogs, -> (SELECT -> GROUP_CONCAT(DISTINCT syslog_events.type_name) -> FROM -> syslog_events -> WHERE -> syslog_events.location_serial = turbine_serial -> AND state = 'Active' -> AND (severity = 'fault' -> OR severity = 'emergency')) AS types, -> (SELECT -> DATEDIFF(CURDATE(), MAX(after)) -> FROM -> rest_measurement_registry -> WHERE -> rest_measurement_registry.serial = turbine_serial) AS measurment_is_delayed -> FROM -> tcm_offline.site_configuration -> JOIN turbine_information ON site_index = mysqld_multi_index -> WHERE -> site_index = 2 AND site_index IN (1 , 2); +------------+-------+-----------+--------------+--------------+---------------+---------+--------------------------------------------------------------------------------------+-----------------------+ | site_index | wt_id | wt_serial | wt_turbine | wt_name | unack_syslogs | syslogs | types | measurment_is_delayed | +------------+-------+-----------+--------------+--------------+---------------+---------+--------------------------------------------------------------------------------------+-----------------------+ | 2 | 5 | 207643Nac | MSYS_NACELLE | MSYS_NACELLE | 5 | 5 | Modbus-INSMB sensor communication fault,Not in Sync,Measurement Configuration Issues | 15 | +------------+-------+-----------+--------------+--------------+---------------+---------+--------------------------------------------------------------------------------------+-----------------------+ 1 row in set (0.01 sec) MariaDB [tcm_offline]> SELECT -> * -> FROM -> (SELECT -> site_index, -> turbine_id AS wt_id, -> turbine_serial AS wt_serial, -> turbine_name AS wt_turbine, -> display_name AS wt_name, -> (SELECT -> SUM(CASE -> WHEN -> (severity = 'fault' -> OR severity = 'emergency') -> AND acknowledged = 'no' -> AND syslog_events.state = 'active' -> THEN -> 1 -> ELSE 0 -> END) -> FROM -> syslog_events -> WHERE -> syslog_events.location_serial = turbine_serial) AS unack_syslogs, -> (SELECT -> SUM(CASE -> WHEN -> (severity = 'fault' -> OR severity = 'emergency') -> AND syslog_events.state = 'active' -> THEN -> 1 -> ELSE 0 -> END) -> FROM -> syslog_events -> WHERE -> syslog_events.location_serial = turbine_serial) AS syslogs, -> (SELECT -> GROUP_CONCAT(DISTINCT syslog_events.type_name) -> FROM -> syslog_events -> WHERE -> syslog_events.location_serial = turbine_serial -> AND state = 'Active' -> AND (severity = 'fault' -> OR severity = 'emergency')) AS types, -> (SELECT -> DATEDIFF(CURDATE(), MAX(after)) -> FROM -> rest_measurement_registry -> WHERE -> rest_measurement_registry.serial = turbine_serial) AS measurment_is_delayed -> FROM -> tcm_offline.site_configuration -> JOIN turbine_information ON site_index = mysqld_multi_index -> WHERE -> site_index = 2 AND site_index IN (1 , 2)) AS greens -> LEFT JOIN -> (SELECT -> SUBSTRING_INDEX(SUBSTRING_INDEX(MeasurementKey, '/', 2), '/', - 1) AS turbine, -> IFNULL(MAX(IF(AckStatus = 'UnAck', IF(ISNULL(ToTime), CASE -> WHEN -> AlarmType LIKE '%Red%' -> OR AlarmType LIKE 'Overrun' -> THEN -> 8 -> WHEN AlarmType LIKE '%Yellow%' THEN 7 -> WHEN AlarmType LIKE 'Blue%' THEN 6 -> ELSE 0 -> END, 2), IF(ISNULL(ToTime), CASE -> WHEN -> AlarmType LIKE '%Red%' -> OR AlarmType LIKE 'Overrun' -> THEN -> 5 -> WHEN AlarmType LIKE '%Yellow%' THEN 4 -> WHEN AlarmType LIKE 'Blue%' THEN 3 -> ELSE 0 -> END, 1))), - 1) AS severity -> FROM -> alarm_events -> WHERE -> site_index = 2 AND site_index IN (1 , 2) -> GROUP BY turbine) AS alarms ON greens.wt_turbine = alarms.turbine -> ; +------------+-------+-----------+--------------+--------------+---------------+---------+--------------------------------------------------------------------------------------+-----------------------+--------------+----------+ | site_index | wt_id | wt_serial | wt_turbine | wt_name | unack_syslogs | syslogs | types | measurment_is_delayed | turbine | severity | +------------+-------+-----------+--------------+--------------+---------------+---------+--------------------------------------------------------------------------------------+-----------------------+--------------+----------+ | 2 | 5 | 207643Nac | MSYS_NACELLE | MSYS_NACELLE | 5 | 5 | Modbus-INSMB sensor communication fault,Not in Sync,Measurement Configuration Issues | 15 | MSYS_NACELLE | 8 | +------------+-------+-----------+--------------+--------------+---------------+---------+--------------------------------------------------------------------------------------+-----------------------+--------------+----------+ 1 row in set (0.00 sec) MariaDB [tcm_offline]> SELECT -> * -> FROM -> (SELECT -> site_index, -> turbine_id AS wt_id, -> turbine_serial AS wt_serial, -> turbine_name AS wt_turbine, -> display_name AS wt_name, -> (SELECT -> SUM(CASE -> WHEN -> (severity = 'fault' -> OR severity = 'emergency') -> AND acknowledged = 'no' -> AND syslog_events.state = 'active' -> THEN -> 1 -> ELSE 0 -> END) -> FROM -> syslog_events -> WHERE -> syslog_events.location_serial = turbine_serial) AS unack_syslogs, -> (SELECT -> SUM(CASE -> WHEN -> (severity = 'fault' -> OR severity = 'emergency') -> AND syslog_events.state = 'active' -> THEN -> 1 -> ELSE 0 -> END) -> FROM -> syslog_events -> WHERE -> syslog_events.location_serial = turbine_serial) AS syslogs, -> (SELECT -> GROUP_CONCAT(DISTINCT syslog_events.type_name) -> FROM -> syslog_events -> WHERE -> syslog_events.location_serial = turbine_serial -> AND state = 'Active' -> AND (severity = 'fault' -> OR severity = 'emergency')) AS types, -> (SELECT -> DATEDIFF(CURDATE(), MAX(after)) -> FROM -> rest_measurement_registry -> WHERE -> rest_measurement_registry.serial = turbine_serial) AS measurment_is_delayed -> FROM -> tcm_offline.site_configuration -> JOIN turbine_information ON site_index = mysqld_multi_index -> WHERE -> site_index = 2 AND site_index IN (1 , 2)) AS greens -> LEFT JOIN -> (SELECT -> SUBSTRING_INDEX(SUBSTRING_INDEX(MeasurementKey, '/', 2), '/', - 1) AS turbine, -> IFNULL(MAX(IF(AckStatus = 'UnAck', IF(ISNULL(ToTime), CASE -> WHEN -> AlarmType LIKE '%Red%' -> OR AlarmType LIKE 'Overrun' -> THEN -> 8 -> WHEN AlarmType LIKE '%Yellow%' THEN 7 -> WHEN AlarmType LIKE 'Blue%' THEN 6 -> ELSE 0 -> END, 2), IF(ISNULL(ToTime), CASE -> WHEN -> AlarmType LIKE '%Red%' -> OR AlarmType LIKE 'Overrun' -> THEN -> 5 -> WHEN AlarmType LIKE '%Yellow%' THEN 4 -> WHEN AlarmType LIKE 'Blue%' THEN 3 -> ELSE 0 -> END, 1))), - 1) AS severity -> FROM -> alarm_events -> WHERE -> site_index = 2 AND site_index IN (1 , 2) -> GROUP BY turbine) AS alarms ON greens.wt_turbine = alarms.turbine -> ORDER BY measurment_is_delayed DESC , severity DESC; ERROR 2006 (HY000): MySQL server has gone away No connection. Trying to reconnect... Connection id: 4 Current database: tcm_offline ERROR 2013 (HY000): Lost connection to MySQL server during query MariaDB [tcm_offline]>