在PostgreSQL中双重对等 [英] equivalence of from dual in postgreSQL

问题描述

 <$ c 
我使用hibernate和oracle使用hibernate和oracle使用这段代码： 
 
  $ c> if（null！= sessionFactory）{
 Session s = currentSession.get（）; $（b）b 
 if（（null == s）||！s.isOpen（））{
 s = sessionFactory.openSession（）; 
 currentSession.set（s）; 
} else {
 try {
 HibernateWork hibernateWork = new HibernateWork（SELECT 1 FROM DUAL）; 
 s.doWork（hibernateWork）; 
} catch（Exception e）{
 
 s = sessionFactory.openSession（）; 
 currentSession.set（s）; 
} 
} 
 
 return s; 
} 
  

我想用postgreSQL做同样的事情

但PostgreSQL不支持'FROM dual'语法

我想知道postgreSQL中 dual 的等价性

解决方案

完全不需要 FROM 子句。只需 SELECT 1 即可。

I work with hibernate and oracle

I used this code :

 if (null != sessionFactory) {
            Session s = currentSession.get();

            if ((null == s) || !s.isOpen()) {
                s = sessionFactory.openSession();
                currentSession.set(s);
            } else {
                try {
                    HibernateWork hibernateWork = new HibernateWork("SELECT 1 FROM DUAL");
                    s.doWork(hibernateWork);
                } catch (Exception e) {

                    s = sessionFactory.openSession();
                    currentSession.set(s);
                }
            }

            return s;
        }

I want to do the same thing with postgreSQL

but PostgreSQL does NOT support the ‘FROM dual’ syntax

I want to know equivalence of dual in postgreSQL

解决方案

You don't need a FROM clause at all. Just SELECT 1 will do it.

这篇关于在PostgreSQL中双重对等的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！