postgreSQL中函数json_populate_recordset的参数null::myrowtype如何使用

postgresql可以对json数据进行操作，其中json_populate_recordset()函数可以将json数据转化为表，说明文档中该函数参数如下：

son_populate_recordset(base anyelement,from_json json) jsonb_populate_recordset(base anyelement,from_json jsonb)	setof anyelement	Expands the outermost array of objects infrom_jsonto a set of rows whose columns match the record type defined bybase(see note below).	select * from json_populate_recordset(null::myrowtype,'[{"a":1,"b":2},{"a":3,"b":4}]')	a | b ---+--- 1 | 2 3 | 4

其中参数null::myrowtype,是已存在表的表名，调用如下：

select * from json_populate_recordset(null::"poiarray",'[{"distance":"42","direction":"East","tel":"0731-88876770","name":"中南大学北校区出版社","weight":"0.0","typecode":"141105","longitude":"112.932278","address":"麓山南路932 号中南大学","latitude":"28.169033","type":"科教文化服务;传媒机构;出版社","poiid":"B02DB05LP4"},{"distance":"155","direction":"SouthEast","tel":"","name":"中国银行(中南大学支行)","typecode":"160104","longitude":"112.932647","address":"中南大学六食堂后侧","latitude":"28.167892","type":"金融保险服务;银行;中国银行","poiid":"B02DB0UM9V"},{"distance":"102","direction":"West","name":"矿冶园","typecode":"110100","longitude":"112.930803","address":"麓山南路932号中南大学","latitude":"28.169026","type":"风景名胜;公园广场;公园广场","poiid":"B0FFFZ13U8"},{"distance":"196","direction":"SouthWest","name":"中南大学北校区商学院","typecode":"141201","longitude":"112.93034","latitude":"28.167933","type":"科教文化服务;学校;高等院校","poiid":"B02DB104AT"},{"distance":"126","name":"中南大学北校区地球科学与信息物理学院","longitude":"112.930726","latitude":"28.168536","poiid":"B02DB107ER"}]');

对于null::"poiarray"参数，表poiarray必须存在，其结构与json数据相对应，即

create table poiarray(
		distance varchar,direction  varchar,tel  varchar,name  varchar,weight  varchar,typecode  varchar,longitude  varchar,address  varchar,latitude  varchar,type varchar,poiid varchar
);

执行结果如下