SQL Server遍历表中记录的方法
SQL Server遍历表中记录的方法遍历表有下面几种方法
1、使用游标
2、使用表变量
3、使用临时表
下面通过一个简单实例分别介绍三种实现形式
一、原始数据如图
二、需求
给HR.Employees表，fullname 列赋值，其值为 firstname+lastname
为了演示表的遍历，忽略 UPDATE HR.Employees SET fullname= firstname+' '+lastname; 的实现方式
三、使用游标
使用游标的代码主要有以下几个步骤，声明游标，打开游标，使用游标，关闭游标和释放游标。
-- 方法1：游标
-- 声明变量
DECLARE
@empid AS INT,
@firstname AS NVARCHAR(10),
@lastname AS NVARCHAR(20);
-- 声明游标
DECLARE C_Employees CURSOR FAST_FORWARD FOR
SELECT empid,firstname,lastname
FROM HR.Employees
ORDER BY empid;
OPEN C_Employees;
-- 取第一条记录
FETCH NEXT FROM C_Employees INTO @empid,@firstname,@lastname;
WHILE @@FETCH_STATUS=0
BEGIN
-- 操作
UPDATE HR.Employees SET fullname= @firstname+' '+@lastname WHERE empid=@empid;
-- 取下一条记录
FETCH NEXT FROM C_Employees INTO @empid,@firstname,@lastname;
END
-- 关闭游标
CLOSE C_Employees;
-- 释放游标
DEALLOCATE C_Employees;
四、使用表变量
-- 方法2：使用表变量
-- 声明表变量
DECLARE @temp TABLE
(
empid INT,
firstname NVARCHAR(10),
lastname NVARCHAR(20)
);
-- 将源表中的数据插入到表变量中
INSERT INTO @temp(empid, firstname, lastname )
SELECT empid,firstname,lastname FROM HR.Employees
ORDER BY empid;
-- 声明变量
DECLARE
@empid AS INT,
@firstname AS NVARCHAR(10),
@lastname AS NVARCHAR(20);
WHILE EXISTS(SELECT empid FROM @temp)
BEGIN
-- 也可以使用top 1
SET ROWCOUNT 1
SELECT @empid= empid, @firstname= firstname,@lastname= lastname FROM @temp;
UPDATE HR.Employees SET fullname= @firstname+' '+@lastname WHERE empid=@empid;
SET ROWCOUNT 0
DELETE FROM @temp WHERE empid=@empid;
END
五、使用临时表
-- 方法3：使用临时表
-- 创建临时表
IF OBJECT_ID('tempdb.dbo.#tempemployees','U') IS NOT NULL DROP TABLE dbo.#tempemployees;
GO
SELECT empid,firstname,lastname
INTO dbo.#tempemployees
FROM HR.Employees
ORDER BY empid;
--SELECT * FROM dbo.#tempemployees;
-- 声明变量
DECLARE
@empid AS INT,
@firstname AS NVARCHAR(10),
@lastname AS NVARCHAR(20);
WHILE EXISTS(SELECT empid FROM dbo.#tempemployees)
BEGIN
-- 也可以使用top 1
SET ROWCOUNT 1
SELECT @empid= empid, @firstname= firstname,@lastname= lastname FROM dbo.#tempemployees;
UPDATE HR.Employees SET fullname= @firstname+' '+@lastname WHERE empid=@empid;
SET ROWCOUNT 0
DELETE FROM dbo.#tempemployees WHERE empid=@empid;
END