如何在创建类型中使用原始Postgres input/output_函数?

你可以创建一个类型,就像 smallint

CREATE TYPE myint;

CREATE FUNCTION myintin(cstring) RETURNS myint
   LANGUAGE internal IMMUTABLE STRICT PARALLEL SAFE AS 'int2in';

CREATE FUNCTION myintout(myint) RETURNS cstring
   LANGUAGE internal IMMUTABLE STRICT PARALLEL SAFE AS 'int2out';

CREATE FUNCTION myintrecv(internal) RETURNS myint
   LANGUAGE internal IMMUTABLE STRICT PARALLEL SAFE AS 'int2recv';

CREATE FUNCTION myintsend(myint) RETURNS bytea
   LANGUAGE internal IMMUTABLE STRICT PARALLEL SAFE AS 'int2send';

CREATE TYPE myint (
   INPUT = myintin,
   OUTPUT = myintout,
   RECEIVE = myintrecv,
   SEND = myintsend,
   LIKE = smallint,
   CATEGORY = 'N',
   PREFERRED = FALSE,
   DELIMITER = ',',
   COLLATABLE = FALSE
);

如果要在算术表达式中使用强制转换,则必须定义对其他数值类型的强制转换。

如果您还添加了来自 varchar text ),但请注意,在类型解析期间,创建太多类型转换可能会导致歧义和令人惊讶的行为。这就是为什么PostgreSQL 8.3中删除了许多类型转换的原因,请参阅 release notes .