SQL 高级用法续

将数据库表的字段类型从datatime全部改为varchar(30),是sql2k的数据库：

create procedure my_pro (@tname varchar(50),@cname varchar(50))
as

declare @str varchar(500)
declare @tname1 varchar(50)
declare @cname1 varchar(50)

select @tname1=@tname
select @cname1=@cname

begin
set @str ='alter table '+@tname1+' alter column '+@cname1+' varchar(90)'
exec(@str)
end;

示例
A. 使用带有复杂 SELECT 语句的简单过程
下面的存储过程从四个表的联接中返回所有作者（提供了姓名）、出版的书籍以及出版社。该存储过程不

使用任何参数。
USE pubs
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'au_info_all' AND type = 'P')
DROP PROCEDURE au_info_all
GO
CREATE PROCEDURE au_info_all
AS
SELECT au_lname, au_fname, title, pub_name
FROM authors a INNER JOIN titleauthor ta
ON a.au_id = ta.au_id INNER JOIN titles t
ON t.title_id = ta.title_id INNER JOIN publishers p
ON t.pub_id = p.pub_id
GO
au_info_all 存储过程可以通过以下方法执行：
EXECUTE au_info_all
-- Or
EXEC au_info_all
如果该过程是批处理中的第一条语句，则可使用：
au_info_all
B. 使用带有参数的简单过程
下面的存储过程从四个表的联接中只返回指定的作者（提供了姓名）、出版的书籍以及出版社。该存储过

程接受与传递的参数精确匹配的值。
USE pubs
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'au_info' AND type = 'P')
DROP PROCEDURE au_info
GO
USE pubs
GO
CREATE PROCEDURE au_info
@lastname varchar(40),
@firstname varchar(20)
AS
SELECT au_lname, au_fname, title, pub_name
FROM authors a INNER JOIN titleauthor ta
ON a.au_id = ta.au_id INNER JOIN titles t
ON t.title_id = ta.title_id INNER JOIN publishers p
ON t.pub_id = p.pub_id
WHERE au_fname = @firstname
AND au_lname = @lastname
GO
au_info 存储过程可以通过以下方法执行：
EXECUTE au_info 'Dull', 'Ann'
-- Or
EXECUTE au_info @lastname = 'Dull', @firstname = 'Ann'
-- Or
EXECUTE au_info @firstname = 'Ann', @lastname = 'Dull'
-- Or
EXEC au_info 'Dull', 'Ann'
-- Or
EXEC au_info @lastname = 'Dull', @firstname = 'Ann'
-- Or
EXEC au_info @firstname = 'Ann', @lastname = 'Dull'
如果该过程是批处理中的第一条语句，则可使用：
au_info 'Dull', 'Ann'
-- Or
au_info @lastname = 'Dull', @firstname = 'Ann'
-- Or
au_info @firstname = 'Ann', @lastname = 'Dull'
C. 使用带有通配符参数的简单过程
下面的存储过程从四个表的联接中只返回指定的作者（提供了姓名）、出版的书籍以及出版社。该存储过

程对传递的参数进行模式匹配，如果没有提供参数，则使用预设的默认值。
USE pubs
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'au_info2' AND type = 'P')
DROP PROCEDURE au_info2
GO
USE pubs
GO
CREATE PROCEDURE au_info2
@lastname varchar(30) = 'D%',
@firstname varchar(18) = '%'
AS
SELECT au_lname, au_fname, title, pub_name
FROM authors a INNER JOIN titleauthor ta
ON a.au_id = ta.au_id INNER JOIN titles t
ON t.title_id = ta.title_id INNER JOIN publishers p
ON t.pub_id = p.pub_id
WHERE au_fname LIKE @firstname
AND au_lname LIKE @lastname
GO
au_info2 存储过程可以用多种组合执行。下面只列出了部分组合：
EXECUTE au_info2
-- Or
EXECUTE au_info2 'Wh%'
-- Or
EXECUTE au_info2 @firstname = 'A%'
-- Or
EXECUTE au_info2 '[CK]ars[OE]n'
-- Or
EXECUTE au_info2 'Hunter', 'Sheryl'
-- Or
EXECUTE au_info2 'H%', 'S%'
D. 使用 OUTPUT 参数
OUTPUT 参数允许外部过程、批处理或多条 Transact-SQL 语句访问在过程执行期间设置的某个值。下面

的示例创建一个存储过程
(titles_sum)，并使用一个可选的输入参数和一个输出参数。
首先，创建过程：
USE pubs
GO
IF EXISTS(SELECT name FROM sysobjects
WHERE name = 'titles_sum' AND type = 'P')
DROP PROCEDURE titles_sum
GO
USE pubs
GO
CREATE PROCEDURE titles_sum @@TITLE varchar(40) = '%', @@SUM money
OUTPUT
AS
SELECT 'Title Name' = title
FROM titles
WHERE title LIKE @@TITLE
SELECT @@SUM = SUM(price)
FROM titles
WHERE title LIKE @@TITLE
GO
接下来，将该 OUTPUT 参数用于控制流语言。

说明 OUTPUT 变量必须在创建表和使用该变量时都进行定义。

参数名和变量名不一定要匹配，不过数据类型和参数位置必须匹配（除非使用 @@SUM = variable 形式）

。
DECLARE @@TOTALCOST money
EXECUTE titles_sum 'The%', @@TOTALCOST OUTPUT
IF @@TOTALCOST < 200
BEGIN
PRINT ' '
PRINT 'All of these titles can be purchased for less than $200.'
END
ELSE
SELECT 'The total cost of these titles is $'
+ RTRIM(CAST(@@TOTALCOST AS varchar(20)))
下面是结果集：
Title Name

------------------------------------------------------------------------

The Busy Executive's Database Guide
The Gourmet Microwave
The Psychology of Computer Cooking
(3 row(s) affected)
Warning, null value eliminated from aggregate.

All of these titles can be purchased for less than $200.
E. 使用 OUTPUT 游标参数
OUTPUT 游标参数用来将存储过程的局部游标传递回调用批处理、存储过程或触发器。
首先，创建以下过程，在 titles 表上声明并打开一个游标：
USE pubs
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'titles_cursor' and type = 'P')
DROP PROCEDURE titles_cursor
GO
CREATE PROCEDURE titles_cursor @titles_cursor CURSOR VARYING OUTPUT
AS
SET @titles_cursor = CURSOR
FORWARD_ONLY STATIC FOR
SELECT *
FROM titles
OPEN @titles_cursor
GO
接下来，执行一个批处理，声明一个局部游标变量，执行上述过程以将游标赋值给局部变量，然后从该游

标提取行。
USE pubs
GO
DECLARE @MyCursor CURSOR
EXEC titles_cursor @titles_cursor = @MyCursor OUTPUT
WHILE (@@FETCH_STATUS = 0)
BEGIN
FETCH NEXT FROM @MyCursor
END
CLOSE @MyCursor
DEALLOCATE @MyCursor
GO
F. 使用 WITH RECOMPILE 选项
如果为过程提供的参数不是典型的参数，并且新的执行计划不应高速缓存或存储在内存中，WITH

RECOMPILE 子句会很有帮助。
USE pubs
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'titles_by_author' AND type = 'P')
DROP PROCEDURE titles_by_author
GO
CREATE PROCEDURE titles_by_author @@LNAME_PATTERN varchar(30) = '%'
WITH RECOMPILE
AS
SELECT RTRIM(au_fname) + ' ' + RTRIM(au_lname) AS 'Authors full
name',
title AS Title
FROM authors a INNER JOIN titleauthor ta
ON a.au_id = ta.au_id INNER JOIN titles t
ON ta.title_id = t.title_id
WHERE au_lname LIKE @@LNAME_PATTERN
GO
G. 使用 WITH ENCRYPTION 选项
WITH ENCRYPTION 子句对用户隐藏存储过程的文本。下例创建加密过程，使用 sp_helptext
系统存储过程获取关于加密过程的信息，然后尝试直接从 syscomments 表中获取关于该过程的信息。
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'encrypt_this' AND type = 'P')
DROP PROCEDURE encrypt_this
GO
USE pubs
GO
CREATE PROCEDURE encrypt_this
WITH ENCRYPTION
AS
SELECT *
FROM authors
GO
EXEC sp_helptext encrypt_this
下面是结果集：
The object's comments have been encrypted.
接下来，选择加密存储过程内容的标识号和文本。
SELECT c.id, c.text
FROM syscomments c INNER JOIN sysobjects o
ON c.id = o.id
WHERE o.name = 'encrypt_this'
下面是结果集：

说明 text 列的输出显示在单独一行中。执行时，该信息将与 id 列信息出现在同一行中。

id text

----------
------------------------------------------------------------
1413580074
?????????????????????????????????

e??????????????????????????????????????????????????????????????????????????
(1 row(s) affected)
H. 创建用户定义的系统存储过程
下面的示例创建一个过程，显示表名以 emp 开头的所有表及其对应的索引。如果没有指定参数，该过程

将返回表名以 sys
开头的所有表（及索引）。
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'sp_showindexes' AND type = 'P')
DROP PROCEDURE sp_showindexes
GO
USE master
GO
CREATE PROCEDURE sp_showindexes
@@TABLE varchar(30) = 'sys%'
AS
SELECT o.name AS TABLE_NAME,
i.name AS INDEX_NAME,
indid AS INDEX_ID
FROM sysindexes i INNER JOIN sysobjects o
ON o.id = i.id
WHERE o.name LIKE @@TABLE
GO
USE pubs
EXEC sp_showindexes 'emp%'
GO
下面是结果集：
TABLE_NAME INDEX_NAME INDEX_ID
---------------- ---------------- ----------------
employee employee_ind 1
employee PK_emp_id 2
(2 row(s) affected)
I. 使用延迟名称解析
下面的示例显示四个过程以及延迟名称解析的各种可能使用方式。尽管引用的表或列在编译时不存在，但

每个存储过程都可创建。
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'proc1' AND type = 'P')
DROP PROCEDURE proc1
GO
-- Creating a procedure on a nonexistent table.
USE pubs
GO
CREATE PROCEDURE proc1
AS
SELECT *
FROM does_not_exist
GO
-- Here is the statement to actually see the text of the procedure.
SELECT o.id, c.text
FROM sysobjects o INNER JOIN syscomments c
ON o.id = c.id
WHERE o.type = 'P' AND o.name = 'proc1'
GO
USE master
GO
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'proc2' AND type = 'P')
DROP PROCEDURE proc2
GO
-- Creating a procedure that attempts to retrieve information from a
-- nonexistent column in an existing table.
USE pubs
GO
CREATE PROCEDURE proc2
AS
DECLARE @middle_init char(1)
SET @middle_init = NULL
SELECT au_id, middle_initial = @middle_init
FROM authors
GO
-- Here is the statement to actually see the text of the procedure.
SELECT o.id, c.text
FROM sysobjects o INNER JOIN syscomments c
ON o.id = c.id
WHERE o.type = 'P' and o.name = 'proc2'