SQL连接类
using System;
using System.Collections;
using System.Collections.Specialized;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Runtime.InteropServices;
using System.Windows.Forms;
namespace DAL
{
public class DataControl
{
public static string connectionString = "server=" + SystemSet.getServerSet_ServerIP() + ";uid=" + SystemSet.getServerSet_ServerUser() + ";pwd=" + SystemSet.getServerSet_ServerPass() + ";database=" + SystemSet.getServerSet_ServerDataBase() + "";
/// <summary>
/// 初始化 /// </summary>
public DataControl()
{
}
/// <summary>
/// 无参数，测试数据库连接是否设置合理。 /// </summary>
/// <returns>是否连接成功</returns>
public static bool checkconn()
{
try
{
SqlConnection conn = new SqlConnection(connectionString);
conn.Open();
return true;
}
&
相关文档：
1、触发器的概念
触发器也是一种带名的PL/SQL块。触发器类似于过程和函数，因为它们都是拥有声明、执行和异常处理过程的带名PL/SQL块。与包类似，触发器必须存储在数据库中并且不能被块进行本地化声明。
对于触发器而言，当触发事件发生的时候就会显式地执行该触发器，并且触发器不接受参数。
创建触发器的语法� ......
Subquery: (single-row subqueries and multi-rows subqueries).
select select_list
from table
where expr operator (select select_list from table);
single-row subqueries operator: =, >, >=, <, <=, <>
e.g.:
1. select department_id, min(salary) from employees group by department_id ......
constraint Example:
1. grammer:
create table [schema.]table
(column datatype [DEFAULT expr]
[column_constraint], ...
[table_constraint] [,......]);
2. example of a column_level constraint:
create table empl ......
Differring Constraints:
Constraints can have the following attributes: DEFFERRABLE / NOT DEFFERRABLE, INITIALLY DEFFERRED / INITIALLY IMMEDIATE.
e.g.:
alter table dept2 add constraint dept2_id_pk primary key (department_id) deferrable initially deferred; // deferring constraint on creation. ......
(注:outer的意思就是"没有关联上的行"。)
1.cross join 全外连接(笛卡尔乘积)
SELECT A.*, B.* from A FULL OUTER JOIN B ON A.ID = B.ID
2.inner join 内连接(在笛卡尔乘积的结果集中去掉不符合连接条件的行)
SELECT A.* from A INNER JOIN B ON A.ID=B.ID
3.left outer join 左外连接(在inner join的结� ......
