ms.xxx_time」列は、GROUP BY句で表示するか、集約関数で使用する必要があります。

 SELECT
        avg() as ,
        max() as ,
        min() as ,
        count() as ,
        sum() as ,
        to_char(xxx,
        'yyyy-MM-dd hh24:MI:ss') 
    FROM
        metrics  
    where
        metrics.tag = ?  
        and zzz_time between ? and ?
2018-07-24 09:29:56.785 WARN 9768 --- [nio-8080-exec-4] o.h.engine.jdbc.spi.SqlExceptionHelper : SQL Error: 0, SQLState: 42803
2018-07-24 09:29:56.785 ERROR 9768 --- [nio-8080-exec-4] o.h.engine.jdbc.spi.SqlExceptionHelper : ERROR: column "metrics.server_time& quot; must appear in the GROUP BY clause or be used in an aggregate function
  Location: 147
2018-07-24 09:29:56.938 ERROR 9768 --- [nio-8080-exec-4] o.a.c.c.C. [. [. [/]. [dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.InvalidDataAccessResourceUsageException: could not extract ResultSet; SQL [n/a]; nested exception is org. hibernate.exception.SQLGrammarException: could not extract ResultSet] with root cause

org.postgresql.util.PSQLException: ERROR: column "metrics.server_time" must appear in the GROUP BY clause or be used in an aggregate function
  Location: 147

<イグ

集計機能があるため、group byを使用します。