PostgresException: '40P01: deadlock detected'

[HGinnerup]

Query executed:

EXPLAIN SELECT
       happiness_poorer.country AS poorer_name,
       happiness_poorer.happiness_score AS poorer_happy,
       gdp_less.gdp AS poorer_gdp,
       happiness_richer.country AS richer_name,
       happiness_richer.happiness_score AS richer_happy,
       gdp_more.gdp AS richer_gdp
    FROM yearly_gdp gdp_more
    JOIN yearly_gdp gdp_less
        ON gdp_less.gdp < gdp_more.gdp AND
           gdp_less.year = gdp_more.year
    JOIN countries country_poorer ON
        country_poorer.code = gdp_less.country_code
    JOIN countries country_richer ON
        country_richer.code = gdp_more.country_code
    JOIN world_happiness_2022 happiness_poorer ON
        happiness_poorer.country = country_poorer.name
    JOIN world_happiness_2022 happiness_richer ON
        happiness_richer.country = country_richer.name
    WHERE
          gdp_less.year = 2020 AND
          happiness_poorer.happiness_score > happiness_richer.happiness_score;

Exception

Npgsql.PostgresException
  HResult=0x80004005
  Message=40P01: deadlock detected

POSITION: 639
DETAIL: Detail redacted as it may contain sensitive data. Specify 'Include Error Detail' in the connection string to include this information.
  Source=Npgsql
  StackTrace:
   at Npgsql.Internal.NpgsqlConnector.<<ReadMessage>g__ReadMessageLong|211_0>d.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Npgsql.NpgsqlDataReader.<NextResult>d__47.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Npgsql.NpgsqlDataReader.NextResult()
   at Npgsql.NpgsqlCommand.<ExecuteReader>d__116.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Npgsql.NpgsqlCommand.<ExecuteReader>d__116.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Npgsql.NpgsqlCommand.ExecuteReader(CommandBehavior behavior)
   at System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior)
   at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior)
   at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet)
   at DatabaseConnector.Connectors.BaseDbConnector`3.<>c__DisplayClass12_1.<CallQueryAsync>b__0() in C:\Users\Henrik\source\repos\P6\Jantimizer\DatabaseConnector\Connectors\BaseDbConnector.cs:line 67
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state)

  This exception was originally thrown at this call stack:
    [External Code]
    DatabaseConnector.Connectors.BaseDbConnector<Connector, Command, Adapter>.CallQueryAsync.AnonymousMethod__0() in BaseDbConnector.cs
    [External Code]`