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：
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)","weight":"0.0","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","tel":"","name":"矿冶园","weight":"0.0","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","tel":"","name":"中南大学北校区商学院","weight":"0.0","typecode":"141201","longitude":"112.93034","address":"麓山南路932号中南大学","latitude":"28.167933","type":"科教文化服务;学校;高等院校","poiid":"B02DB104AT"},{"distance":"126","direction":"SouthWest","tel":"","name":"中南大学北校区地球科学与信息物理学院","weight":"0.0","typecode":"141201","longitude":"112.930726","address":"麓山南路932号中南大学","latitude":"28.168536","type":"科教文化服务;学校;高等院校","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
);