A. 在简单的游标中使用 FETCH
下例为 authors 表中姓以字母 B 开头的行声明了一个简单的游标,并使用 FETCH NEXT 逐个提取这些行。FETCH 语句以单行结果集形式返回由 DECLARE CURSOR 指定的列的值。
DECLARE authors_cursor CURSOR FOR SELECT au_lname FROM authors WHERE au_lname LIKE "B%" ORDER BY au_lname OPEN authors_cursor -- Perform the first fetch. FETCH NEXT FROM authors_cursor -- Check @@FETCH_STATUS to see if there are any more rows to fetch. WHILE @@FETCH_STATUS = 0 BEGIN -- This is executed as long as the previous fetch succeeds. FETCH NEXT FROM authors_cursor END CLOSE authors_cursor DEALLOCATE authors_cursor GO
au_lname
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Bennet
au_lname
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Blotchet-Halls
au_lname
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B. 使用 FETCH 将值存入变量
下例与上例相似,但 FETCH 语句的输出存储于局部变量而不是直接返回给客户端。PRINT 语句将变量组合成单一字符串并将其返回到客户端。
-- Declare the variables to store the values returned by FETCH. DECLARE @au_lname varchar(40), @au_fname varchar(20) DECLARE authors_cursor CURSOR FOR SELECT au_lname, au_fname FROM authors WHERE au_lname LIKE "B%" ORDER BY au_lname, au_fname OPEN authors_cursor -- Perform the first fetch and store the values in variables. -- Note: The variables are in the same order as the columns -- in the SELECT statement. FETCH NEXT FROM authors_cursor INTO @au_lname, @au_fname -- Check @@FETCH_STATUS to see if there are any more rows to fetch. WHILE @@FETCH_STATUS = 0 BEGIN -- Concatenate and display the current values in the variables. PRINT "Author: " + @au_fname + " " + @au_lname -- This is executed as long as the previous fetch succeeds. FETCH NEXT FROM authors_cursor INTO @au_lname, @au_fname END CLOSE authors_cursor DEALLOCATE authors_cursor GO
C. 声明 SCROLL 游标并使用其它 FETCH 选项
下例创建一个 SCROLL 游标,使其通过 LAST、PRIOR、RELATIVE 和 ABSOLUTE 选项支持所有滚动能力。
-- Execute the SELECT statement alone to show the -- full result set that is used by the cursor. SELECT au_lname, au_fname FROM authors ORDER BY au_lname, au_fname -- Declare the cursor. DECLARE authors_cursor SCROLL CURSOR FOR SELECT au_lname, au_fname FROM authors ORDER BY au_lname, au_fname OPEN authors_cursor -- Fetch the last row in the cursor. FETCH LAST FROM authors_cursor -- Fetch the row immediately prior to the current row in the cursor. FETCH PRIOR FROM authors_cursor -- Fetch the second row in the cursor. FETCH ABSOLUTE 2 FROM authors_cursor -- Fetch the row that is three rows after the current row. FETCH RELATIVE 3 FROM authors_cursor -- Fetch the row that is two rows prior to the current row. FETCH RELATIVE -2 FROM authors_cursor CLOSE authors_cursor DEALLOCATE authors_cursor GO
au_lname au_fname
---------------------------------------- --------------------
Bennet Abraham
Blotchet-Halls Reginald
Carson Cheryl
DeFrance Michel
del Castillo Innes
Dull Ann
Green Marjorie
Greene Morningstar
Gringlesby Burt
Hunter Sheryl
Karsen Livia
Locksley Charlene
MacFeather Stearns
McBadden Heather
O'Leary Michael
Panteley Sylvia
Ringer Albert
Ringer Anne
Smith Meander
Straight Dean
Stringer Dirk
White Johnson
Yokomoto Akiko
au_lname au_fname
---------------------------------------- --------------------
Yokomoto Akiko
au_lname au_fname
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White Johnson
au_lname au_fname
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Blotchet-Halls Reginald
au_lname au_fname
---------------------------------------- --------------------
del Castillo Innes
au_lname au_fname
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Carson Cheryl