FortiAnalyzer can receive logs and Windows host events directly from endpoints connected to EMS, and you can use FortiAnalyzer to analyze the logs and run reports.
Occasionally an upgrade does not correctly update the SQL database and reporting will cease to function properly due to missing/misnamed columns and/or indexes.

'# exec sql-local rebuild-db' is the first option, but if that does not resolve the issue then deleting and rebuilding of the database is the next step.
Be aware that rebuilding the database is resource and time consuming and the reports as well log view and FortiView will not be fully usable until the rebuild is over.

Remove and re-create the SQL db:

1) Change operation mode to collector (prior 6.2).
# config system global
    set log-mode collector
2) Disable SQL and remove the current database (prior 6.2).
# config system sql
    set status disable
# execute sql-local remove-db      <----- This command does not exist after 6.2.0.
3) Re-enable SQL (prior 6.2).
# config system sql
    set status local
4) Change operation mode back to analyzer (prior 6.2).
# config system global
    set log-mode analyzer
5) Rebuild database.
# exec sql-local rebuild-db
6) Set the following value to rebuild the database with logs from the expected date (this depend on how much Analytics days configured for this ADOM)

For example if 90 days have been requested and it is the 1st of September 2021.
# config system sql
    set start-time <for ex:00:00 2021/06/01>
7) Rebuild database.
# execute sql-local rebuild-db                  <----- Require restart.
# execute sql-local rebuild-adom adomName       <----- Does not require a restart.

Troubleshooting SQL rebuild.
# diag test app sqllogd 4    <----- This will let know which file the rebuilding process is handling at present , it is necessary to run it multiple time to check SQL rebuild status.
# diag sql show db-size       <----- This will show if the DB size increases, if it is run it multiple times a few minutes apart.
# diag sql process list       <----- It is possible sometimes to see a process here with commands like 'Create table'. 'Insert' or mentioning filenames;
# exe tac report
# exe top                   <----- Let it run for 5 min.

(1) The rebuild-db command causes the unit to reboot and the rebuild starts when the unit comes back up.

(2) Use the command 'diag sql status rebuild-db' to show the status of the rebuild.

(3) The time required to rebuild the database depends on the amount of logs stored on the unit.

(4) Although this procedure does not remove any log files it is recommended to backup log files beforehand as a precaution.