Data conversion in the Postgres database

After postgres8.3, the default transitions between field data are canceled. If a data transformation is required, in the Postgres database, we can use "::" To convert the field data into a type. The actual "::" is called by the cast function. exactly what fields can be converted between data?

This problem can be answered only by studying the cast function. The information of the cast function is managed in the System Pg_cast table.

through the query we can get the type of the current can be converted to the following table:

Source Type conversion Destination type

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

Data conversion in the Postgres database