Question

我在SQLite中发现了这种意外行为。似乎SQLite在SQL连接语法中接受任意关键字。如果我不小心输入中立连接而不是自然连接，则会生成笛卡尔积。这是预期的行为，功能还是错误？

select count(*) from pri; -- 22
select count(*) from sec; -- 57458

select count(*) from pri natural join sec; -- 57458 
select count(*) from pri nautral join sec; -- 1264076
select count(*) from pri advanced natural join sec; -- 57458
select count(*) from pri imaginary join sec; -- 1264076

在Debian 6.0上使用SQLite 3.7.3和在Windows 7上使用SQLite 3.7.5进行测试。

要添加：SQLite是一个很好的数据库软件，我推荐它从中小型项目。这是my brief SQLite vs PostgreSQL comparison.

Answer 1

nautral和imaginary被解析为表的别名：

select count(*) from (pri) natural join sec; -- 57458 
select count(*) from (pri AS nautral) join sec; -- 1264076
select count(*) from (pri AS advanced) natural join sec; -- 57458
select count(*) from (pri AS imaginary) join sec; -- 1264076

SQLite接受SQL语法中不存在的连接类型

1 个答案: