postgres 数据库中的数据转换

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