实际上"::"是调用CAST函数的。究竟哪些字段之间可以进行数据转换呢？ 这个问题只要研究一下cast函数就能够得到答案。cast函数的信息在系统pg_cast表里面管理。 通过查询我们可以得到现阶段可以转换的类型对照表如下： 源类型 转换目标类型 int8 int2 int8 int4 int8 float4 int8 float8 int8 numeric int2 int8 int2 int4 int2 float4 int2 float8 int2 numeric int4 int8 int4 int2 int4 float4 int4 float8 int4 numeric float4 int8 float4 int2 float4 int4 float4 float8 float4 numeric float8 int8 float8 int2 float8 int4 float8 float4 float8 numeric numeric int8 numeric int2 numeric int4 numeric float4 numeric float8 int4 bool bool int4 int8 oid int2 oid oid int8 int8 regproc int2 regproc regproc int8 int8 regprocedure int2 regprocedure regprocedure int8 int8 regoper int2 regoper regoper int8 int8 regoperator int2 regoperator regoperator int8 int8 regclass int2 regclass regclass int8 int8 regtype int2 regtype regtype int8 int8 regconfig int2 regconfig regconfig int8 int8 regdictionary int2 regdictionary regdictionary int8 text regclass varchar regclass bpchar text bpchar varchar char text char bpchar char varchar name text name bpchar name varchar text char bpchar char varchar char text name bpchar name varchar name char int4 int4 char abstime date abstime time abstime timestamp abstime timestamptz reltime interval date timestamp date timestamptz time interval time timetz timestamp abstime timestamp date timestamp time timestamp timestamptz timestamptz abstime timestamptz date timestamptz time timestamptz timestamp timestamptz timetz interval reltime interval time timetz time lseg point path point path polygon box point box lseg box polygon box circle polygon point polygon path polygon box polygon circle circle point circle box circle polygon inet cidr int8 bit int4 bit bit int8 bit int4 cidr text inet text bool text text xml cidr varchar inet varchar bool varchar varchar xml cidr bpchar inet bpchar bool bpchar bpchar xml bpchar bpchar varchar varchar time time timestamp timestamp timestamptz timestamptz interval interval timetz timetz bit bit varbit varbit numeric numeric