sql - sql根据最新的外键日期字段选择单行

Question

我有两个 sql 表，alarmMessage并且coordinates. alarmMessage表具有表的外键字段coordinates。alarmMessage我想从其坐标具有最新（最大）gpsDate 字段的表中检索单行。

报警信息：

CREATE TABLE alarmmessage
(
  alarmmessageid bigint NOT NULL,
  mtstrackid character varying(40),
  coordinatesid bigint,
  totaldistance double precision,
  iostatusid bigint,
  alarmstatus character varying(10),
  totalworkingduration integer,
  maintenanceremainingtime integer,
  isread boolean NOT NULL DEFAULT false,
  CONSTRAINT pk_alarmmessageid PRIMARY KEY (alarmmessageid ),
  CONSTRAINT fk_coordinatesid FOREIGN KEY (coordinatesid)
      REFERENCES coordinates (coordinatesid) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT fk_iostatus FOREIGN KEY (iostatusid)
      REFERENCES iostatus (iostatusid) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT fk_mtstrackid FOREIGN KEY (mtstrackid)
      REFERENCES vehicle (mtstrackid) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
)

坐标：

CREATE TABLE coordinates
(
  coordinatesid bigint NOT NULL,
  latitude double precision NOT NULL,
  longitude double precision NOT NULL,
  gpsvalid boolean,
  gpsdate timestamp without time zone,
  bearingangle double precision,
  speed double precision,
  mtstrackid character varying(40),
  altitude double precision,
  CONSTRAINT pk_coordinates PRIMARY KEY (coordinatesid )
)

Answer 1

您可以使用以下 SQL：

SELECT alarmmessage.* FROM alarmmessage
INNER JOIN coordinates ON alarmmessage.coordinatesid = coordinates.coordinatesid
ORDER BY gpsdate DESC
LIMIT 1