类型系统：ANSI SQL（标准）与 Postgres、Oracle、DB2

Question

这是一个非常笼统的问题，我希望找到既熟悉标准又熟悉一些数据库系统的专家。在高层次上，SQL 标准中描述的类型系统与 Postgres、Oracle 或 DB2 中实现的类型系统之间有哪些区别。

我只是在编一些东西（它是不正确的 -- 只是用来显示我感兴趣的比较类型的格式），但是例子可能是这样的：

Standard	Postgres	Oracle
INTERVAL type	Does not exist, closest is TIME	Same as standard.

（顺便说一句，这个问题对DBA来说会更好吗？）

Answer 1

很少有人能够给你一个完整的清单，所以我只告诉你我所知道的，不保证完整性。我也将自己限制在我更了解的数据库中。

对数据库实施的评论描述了与标准的偏差。

SQL standard	PostgreSQL	Oracle	Comments
CHARACTER	✔	empty strings are treated as NULL	weird standard-dictated semantics; avoid
CHARACTER VARYING	✔	empty strings are treated as NULL
CHARACTER LARGE OBJECT	non-standard name text or varchar	✔
NATIONAL CHARACTER	✔	empty strings are treated as NULL	obsolescent
NATIONAL CHARACTER VARYING	✔	empty strings are treated as NULL	obsolescent
NATIONAL CHARACTER LARGE OBJECT	non-standard name text or varchar	empty strings are treated as NULL	obsolescent
BINARY LARGE OBJECT	non-standard name bytea	✔
NUMERIC	✔	✔
DECIMAL	✔	✔	virtually the same as NUMERIC
SMALLINT	✔	✔ (same type as NUMERIC)
INTEGER	✔	✔ (same type as NUMERIC)
BIGINT	✔	✔ (same type as NUMERIC)
FLOAT	✔	✔ (same type as NUMERIC)
REAL	✔	✔ (same type as NUMERIC, but there is also BINARY_FLOAT)
DOUBLE PRECISION	✔	(same type as NUMERIC, but there is also BINARY_DOUBLE)
BOOLEAN	✔	❌ (but allowed in PL/SQL)
DATE	✔	is really a timestamp
TIME	✔	❌
TIME WITH TIME ZONE	✔	❌	semantics unclear; avoid
TIMESTAMP	✔	✔
TIMESTAMP WITH TIME ZONE	semantics differ from the standard	✔
INTERVAL	✔	✔
ROW	composity types	object types
REF	❌	✔ (non-standard syntax)
<type> ARRAY	✔	vararray types
<type> MULTISET	❌	❌
XML	✔	non-standard name XMLTYPE