分类: Mysql/postgreSQL
2015-05-17 22:32:26
原文地址:mysql中的dual表 作者:cenalulu
DUAL
as a dummy
table name in situations where no tables are referenced:
mysql>SELECT 1 + 1 FROM DUAL;
-> 2
DUAL
is purely for the convenience of people
who require that all SELECT
statements should have FROM
and possibly other
clauses. MySQL may ignore the clauses. MySQL does not require
FROM DUAL
if no tables are referenced.