沒有groupby的Postgres計數（使用jpa）

Question

我一直在使用 mariaDB，現在我正在使用 postgres。 我在 JPA 中有一個查詢

select count(<primarykeycolumn>) from tablename where condition

但是 Postgres 給出了一個錯誤，說需要group by子句。

我不想添加組，代碼已啟動並與 mariaDB 一起運行。

下面是錯誤：

Internal Exception: org.postgresql.util.PSQLException: ERROR: column "app_movie_summary.creationdate" must appear in the GROUP BY clause or be used in an aggregate function
  Position: 55
Error Code: 0
Call: SELECT COUNT(id) FROM mytable ORDER BY CREATIONDATE DESC
Query: ReportQuery(name="App_Movie_Summary.findAllByCreationDateCount" referenceClass=App_Movie_Summary sql="SELECT COUNT(Id) FROM mytable ORDER BY CREATIONDATE DESC")
    at org.eclipse.persistence.exceptions.DatabaseException.sqlException(DatabaseException.java:340)
    at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.basicExecuteCall(DatabaseAccessor.java:684)
    at org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeCall(DatabaseAccessor.java:560)
    at org.eclipse.persistence.internal.sessions.AbstractSession.basicExecuteCall(AbstractSession.java:2055)
    at org.eclipse.persistence.sessions.server.ServerSession.executeCall(ServerSession.java:570)
    at org.eclipse.persistence.internal.queries.DatasourceCallQueryMechanism.executeCall(DatasourceCallQueryMechanism.java:242)
    at org.eclipse.persistence.internal.queries.DatasourceCallQueryMechanism.executeCall(DatasourceCallQueryMechanism.java:228)
    at org.eclipse.persistence.internal.queries.DatasourceCallQueryMechanism.executeSelectCall(DatasourceCallQueryMechanism.java:299)
    at org.eclipse.persistence.internal.queries.DatasourceCallQueryMechanism.selectAllRows(DatasourceCallQueryMechanism.java:694)
    at org.eclipse.persistence.internal.queries.ExpressionQueryMechanism.selectAllRowsFromTable(ExpressionQueryMechanism.java:2740)
    at org.eclipse.persistence.internal.queries.ExpressionQueryMechanism.selectAllReportQueryRows(ExpressionQueryMechanism.java:2677)
    at org.eclipse.persistence.queries.ReportQuery.executeDatabaseQuery(ReportQuery.java:852)
    at org.eclipse.persistence.queries.DatabaseQuery.execute(DatabaseQuery.java:904)
    at org.eclipse.persistence.queries.ObjectLevelReadQuery.execute(ObjectLevelReadQuery.java:1134)
    at org.eclipse.persistence.queries.ReadAllQuery.execute(ReadAllQuery.java:460)
    at org.eclipse.persistence.queries.ObjectLevelReadQuery.executeInUnitOfWork(ObjectLevelReadQuery.java:1222)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.internalExecuteQuery(UnitOfWorkImpl.java:2896)
    at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1857)
    at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1839)
    at org.eclipse.persistence.internal.sessions.AbstractSession.executeQuery(AbstractSession.java:1804)
    at org.eclipse.persistence.internal.jpa.QueryImpl.executeReadQuery(QueryImpl.java:258)
    at org.eclipse.persistence.internal.jpa.QueryImpl.getSingleResult(QueryImpl.java:521)
    at org.eclipse.persistence.internal.jpa.EJBQueryImpl.getSingleResult(EJBQueryImpl.java:400)

Answer 1

在 PostgreSQL 中，除非您對未聚合列進行GROUP BY ，否則不能將聚合函數（如count ）與非聚合列（ creationdates ）混合使用。 在這種情況下，看起來您畢竟不需要分組，因為您不需要ORDER BY creationdate 。 順序與count(*)無關。 這個查詢是完全有效的：

SELECT count(*) FROM mytable

如果確實希望包含creationdate ，則必須對其進行GROUP BY 。 當你這樣做時， ORDER BY也再次有意義：

SELECT creationdate, count(*) from mytable
GROUP BY creationdate
ORDER BY creationdate