求最简单的多条件选择方法

select (case field1 when data then isdata else elsedata end) as a from t

示例
A. 使用带有简单 CASE 函数的 SELECT 语句
在 SELECT 语句中，简单 CASE 函数仅检查是否相等，而不进行其它比较。下面的示例使用 CASE 函数更改图书分类显示，以使其更易于理解。USE pubs
GO
SELECT   Category =
      CASE type
         WHEN 'popular_comp' THEN 'Popular Computing'
         WHEN 'mod_cook' THEN 'Modern Cooking'
         WHEN 'business' THEN 'Business'
         WHEN 'psychology' THEN 'Psychology'
         WHEN 'trad_cook' THEN 'Traditional Cooking'
         ELSE 'Not yet categorized'
      END,
   CAST(title AS varchar(25)) AS 'Shortened Title',
   price AS Price
FROM titles
WHERE price IS NOT NULL
ORDER BY type, price
COMPUTE AVG(price) BY type
GO下面是结果集：Category            Shortened Title           Price
------------------- ------------------------- --------------------------
Business            You Can Combat Computer S 2.99
Business            Cooking with Computers: S 11.95
Business            The Busy Executive's Data 19.99
Business            Straight Talk About Compu 19.99                                                                    avg
                                              ==========================
                                              13.73                      Category            Shortened Title           Price
------------------- ------------------------- --------------------------
Modern Cooking      The Gourmet Microwave     2.99
Modern Cooking      Silicon Valley Gastronomi 19.99                                                                    avg
                                              ==========================
                                              11.49                      Category            Shortened Title           Price
------------------- ------------------------- --------------------------
Popular Computing   Secrets of Silicon Valley 20.00
Popular Computing   But Is It User Friendly?  22.95                                                                    avg
                                              ==========================
                                              21.48                      Category            Shortened Title           Price
------------------- ------------------------- --------------------------
Psychology          Life Without Fear         7.00
Psychology          Emotional Security: A New 7.99
Psychology          Is Anger the Enemy?       10.95
Psychology          Prolonged Data Deprivatio 19.99
Psychology          Computer Phobic AND Non-P 21.59                                                                    avg
                                              ==========================
                                              13.50                      Category            Shortened Title           Price
------------------- ------------------------- --------------------------
Traditional Cooking Fifty Years in Buckingham 11.95
Traditional Cooking Sushi, Anyone?            14.99
Traditional Cooking Onions, Leeks, and Garlic 20.95                                                                    avg
                                              ==========================
                                              15.96                      (21 row(s) affected)B. 使用带有简单 CASE 函数和 CASE 搜索函数的 SELECT 语句
在 SELECT 语句中，CASE 搜索函数允许根据比较值在结果集内对值进行替换。下面的示例根据图书的价格范围将价格（money 列）显示为文本注释。USE pubs
GO
SELECT    'Price Category' =
      CASE
         WHEN price IS NULL THEN 'Not yet priced'
         WHEN price < 10 THEN 'Very Reasonable Title'
         WHEN price >= 10 and price < 20 THEN 'Coffee Table Title'
         ELSE 'Expensive book!'
      END,
   CAST(title AS varchar(20)) AS 'Shortened Title'
FROM titles
ORDER BY price
GO下面是结果集：Price Category        Shortened Title
--------------------- --------------------
Not yet priced        Net Etiquette
Not yet priced        The Psychology of Co
Very Reasonable Title The Gourmet Microwav
Very Reasonable Title You Can Combat Compu
Very Reasonable Title Life Without Fear
Very Reasonable Title Emotional Security:
Coffee Table Title    Is Anger the Enemy?
Coffee Table Title    Cooking with Compute
Coffee Table Title    Fifty Years in Bucki
Coffee Table Title    Sushi, Anyone?
Coffee Table Title    Prolonged Data Depri
Coffee Table Title    Silicon Valley Gastr
Coffee Table Title    Straight Talk About
Coffee Table Title    The Busy Executive's
Expensive book!       Secrets of Silicon V
Expensive book!       Onions, Leeks, and G
Expensive book!       Computer Phobic And
Expensive book!       But Is It User Frien (18 row(s) affected)C. 使用带有 SUBSTRING 和 SELECT 的 CASE 函数
下面的示例使用 CASE 和 THEN 生成一个有关作者、图书标识号和每个作者所著图书类型的列表。 USE pubs
SELECT SUBSTRING((RTRIM(a.au_fname) + ' '+
   RTRIM(a.au_lname) + ' '), 1, 25) AS Name, a.au_id, ta.title_id,
   Type =
  CASE
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'BU' THEN 'Business'
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'MC' THEN 'Modern Cooking'
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'PC' THEN 'Popular Computing'
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'PS' THEN 'Psychology'
    WHEN SUBSTRING(ta.title_id, 1, 2) = 'TC' THEN 'Traditional Cooking'
  END
FROM titleauthor ta JOIN authors a ON ta.au_id = a.au_id下面是结果集：Name                      au_id       title_id Type
------------------------- ----------- -------- -------------------
Johnson White             172-32-1176 PS3333   Psychology
Marjorie Green            213-46-8915 BU1032   Business
Marjorie Green            213-46-8915 BU2075   Business
Cheryl Carson             238-95-7766 PC1035   Popular Computing
Michael O'Leary           267-41-2394 BU1111   Business
Michael O'Leary           267-41-2394 TC7777   Traditional Cooking
Dean Straight             274-80-9391 BU7832   Business
Abraham Bennet            409-56-7008 BU1032   Business
Ann Dull                  427-17-2319 PC8888   Popular Computing
Burt Gringlesby           472-27-2349 TC7777   Traditional Cooking
Charlene Locksley         486-29-1786 PC9999   Popular Computing
Charlene Locksley         486-29-1786 PS7777   Psychology
Reginald Blotchet-Halls   648-92-1872 TC4203   Traditional Cooking
Akiko Yokomoto            672-71-3249 TC7777   Traditional Cooking
Innes del Castillo        712-45-1867 MC2222   Modern Cooking
Michel DeFrance           722-51-5454 MC3021   Modern Cooking
Stearns MacFeather        724-80-9391 BU1111   Business
Stearns MacFeather        724-80-9391 PS1372   Psychology
Livia Karsen              756-30-7391 PS1372   Psychology
Sylvia Panteley           807-91-6654 TC3218   Traditional Cooking
Sheryl Hunter             846-92-7186 PC8888   Popular Computing
Anne Ringer               899-46-2035 MC3021   Modern Cooking
Anne Ringer               899-46-2035 PS2091   Psychology
Albert Ringer             998-72-3567 PS2091   Psychology
Albert Ringer             998-72-3567 PS2106   Psychology          (25 row(s) affected)

case when 条件一 then
     when 条件二 then
     .
     .
     .
     else
end

if @a=1 then
begin
end
if @a=2 then
begin
end
..........
也没有更好的方法了

条件执行啊？
case 也不行，只能用if... else...
if @a = 1
begin
end
if @a = 2
begin
end
else
begin
   if ...
   begn
   end
end

调试易

求最简单的多条件选择方法

解决方案 »