与SQL中的NULL比较 [英] Comparisons with NULLs in SQL

问题描述

ANSI-92 SQL要求与NULL的比较评估为虚假"，例如:

ANSI-92 SQL mandates that comparisons with NULL evaluate to "falsy," eg:

SELECT * FROM table WHERE field = NULL
SELECT * FROM table WHERE field != NULL

都将不返回任何行，因为无法像这样比较NULL.相反，必须使用谓词IS NULL和IS NOT NULL:

Will both return no rows because NULL can't be compared like that. Instead, the predicates IS NULL and IS NOT NULL have to be used instead:

SELECT * FROM table WHERE field IS NULL
SELECT * FROM table WHERE field IS NOT NULL

研究表明，Oracle ¹ ，PostgreSQL，MySQL和SQLite均支持ANSI语法.将DB2和Firebird添加到该列表.

Research has shown me that Oracle ¹, PostgreSQL, MySQL and SQLite all support the ANSI syntax. Add to that list DB2 and Firebird.

除了关闭了ANSI_NULLS的SQL Server之外，还有哪些其他RDBMS支持非ANSI语法?

Aside from SQL Server with ANSI_NULLS turned off, what other RDBMS support the non-ANSI syntax?

¹ 整个空字符串= NULL混乱.

¹ The whole empty string = NULL mess notwithstanding.

推荐答案

这里很好比较SQLite，PostgreSQL，Oracle，Informix，DB2，MS-SQL，OCELOT，MySQL 3.23.41，MySQL 4.0.16，Firebird，SQL Anywhere和Borland Interbase中的空处理

Here is a nice comparison of null handling in SQLite, PostgreSQL, Oracle, Informix, DB2, MS-SQL, OCELOT, MySQL 3.23.41, MySQL 4.0.16, Firebird, SQL Anywhere, and Borland Interbase

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