PG_CAST

'e': Only explicit conversion can be performed (using the CAST or :: syntax).
'i': Implicit conversion can be performed.
'a': Both explicit and implicit conversion can be performed between data types.

PG_CAST records the conversion relationship between data types.

**Table 1** PG_CAST columns
Name	Type	Description
oid	oid	Row identifier (hidden attribute, which must be specified).
castsource	oid	OID of the source data type.
casttarget	oid	OID of the target data type.
castfunc	oid	OID of the conversion function. The value 0 indicates that no conversion function is required.
castcontext	"char"	Conversion mode between the source and target data types. 'e': Only explicit conversion can be performed (using the CAST or :: syntax). 'i': Implicit conversion can be performed. 'a': Both explicit and implicit conversion can be performed between data types.
castmethod	"char"	Conversion method. 'f': Conversion is performed using the specified function in the castfunc column. 'b': Binary forcible conversion rather than the specified function in the castfunc column is performed between data types.