SQL語句中關於空記錄sum求和返回null值的處理,兼談case的處理

原創 lifuyun 2018-09-02 00:49

今天做項目寫SQL語句，寫了好多，如下：

SELECT     t0.DRAI_PIPE_NAME_ROAD, t0.DRAI_PIPE_BROAD_NAME, t0.DRAI_PIPE_EROAD_NAME, t1.w1 + t2.w2 + t3.w3 + t4.w4 AS sumfour, t1.w1, t2.w2, t3.w3,
                      t4.w4
FROM         (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                       FROM          sde.TDRAI_PIPE_ST
                       WHERE      (DRAI_PIPE_NAME_ROAD IN
                                                  (SELECT DISTINCT DRAI_PIPE_NAME_ROAD
                                                    FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_1))
                       GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                       ORDER BY DRAI_PIPE_NAME_ROAD) AS t0 LEFT OUTER JOIN
                          (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME, SUM(DRAI_PIPE_LENGTH)
                                                   AS w1
                            FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_2
                            WHERE      (DRAI_PIPE_D1 >= 150) AND (DRAI_PIPE_D1 <= 530)
                            GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                            ORDER BY DRAI_PIPE_NAME_ROAD) AS t1 ON t0.DRAI_PIPE_NAME_ROAD = t1.DRAI_PIPE_NAME_ROAD AND
                      t0.DRAI_PIPE_BROAD_NAME = t1.DRAI_PIPE_BROAD_NAME AND t0.DRAI_PIPE_EROAD_NAME = t1.DRAI_PIPE_EROAD_NAME LEFT OUTER JOIN
                          (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME, SUM(DRAI_PIPE_LENGTH)
                                                   AS w2
                            FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_5
                            WHERE      (DRAI_PIPE_D1 >= 600) AND (DRAI_PIPE_D1 <= 1000)
                            GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                            ORDER BY DRAI_PIPE_NAME_ROAD) AS t2 ON t0.DRAI_PIPE_NAME_ROAD = t2.DRAI_PIPE_NAME_ROAD AND
                      t0.DRAI_PIPE_BROAD_NAME = t2.DRAI_PIPE_BROAD_NAME AND t0.DRAI_PIPE_EROAD_NAME = t2.DRAI_PIPE_EROAD_NAME LEFT OUTER JOIN
                          (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME, SUM(DRAI_PIPE_LENGTH)
                                                   AS w3
                            FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_4
                            WHERE      (DRAI_PIPE_D1 >= 1050) AND (DRAI_PIPE_D1 <= 1400)
                            GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                            ORDER BY DRAI_PIPE_NAME_ROAD) AS t3 ON t0.DRAI_PIPE_NAME_ROAD = t3.DRAI_PIPE_NAME_ROAD AND
                      t0.DRAI_PIPE_BROAD_NAME = t3.DRAI_PIPE_BROAD_NAME AND t0.DRAI_PIPE_EROAD_NAME = t3.DRAI_PIPE_EROAD_NAME LEFT OUTER JOIN
                          (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME, SUM(DRAI_PIPE_LENGTH)
                                                   AS w4
                            FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_3
                            WHERE      (DRAI_PIPE_D1 >= 1500)
                            GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                            ORDER BY DRAI_PIPE_NAME_ROAD) AS t4 ON t0.DRAI_PIPE_NAME_ROAD = t4.DRAI_PIPE_NAME_ROAD AND
                      t0.DRAI_PIPE_BROAD_NAME = t4.DRAI_PIPE_BROAD_NAME AND t0.DRAI_PIPE_EROAD_NAME = t4.DRAI_PIPE_EROAD_NAME

可是出現這樣的情況：求和時有NULL的和值爲NULL了！

經過這樣的處理：

SELECT     t0.DRAI_PIPE_NAME_ROAD, t0.DRAI_PIPE_BROAD_NAME, t0.DRAI_PIPE_EROAD_NAME, CASE WHEN t1.w1 IS NULL
                      THEN 0.0 ELSE t1.w1 END + CASE WHEN t2.w2 IS NULL THEN 0.0 ELSE t2.w2 END + CASE WHEN t3.w3 IS NULL
                      THEN 0.0 ELSE t3.w3 END + CASE WHEN t4.w4 IS NULL THEN 0.0 ELSE t4.w4 END AS sumfour, t1.w1, t2.w2, t3.w3, t4.w4
FROM         (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                       FROM          sde.TDRAI_PIPE_ST
                       WHERE      (DRAI_PIPE_NAME_ROAD IN
                                                  (SELECT DISTINCT DRAI_PIPE_NAME_ROAD
                                                    FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_1))
                       GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                       ORDER BY DRAI_PIPE_NAME_ROAD) AS t0 LEFT OUTER JOIN
                          (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME, SUM(DRAI_PIPE_LENGTH)
                                                   AS w1
                            FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_2
                            WHERE      (DRAI_PIPE_D1 >= 150) AND (DRAI_PIPE_D1 <= 530)
                            GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                            ORDER BY DRAI_PIPE_NAME_ROAD) AS t1 ON t0.DRAI_PIPE_NAME_ROAD = t1.DRAI_PIPE_NAME_ROAD AND
                      t0.DRAI_PIPE_BROAD_NAME = t1.DRAI_PIPE_BROAD_NAME AND t0.DRAI_PIPE_EROAD_NAME = t1.DRAI_PIPE_EROAD_NAME LEFT OUTER JOIN
                          (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME, SUM(DRAI_PIPE_LENGTH)
                                                   AS w2
                            FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_5
                            WHERE      (DRAI_PIPE_D1 >= 600) AND (DRAI_PIPE_D1 <= 1000)
                            GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                            ORDER BY DRAI_PIPE_NAME_ROAD) AS t2 ON t0.DRAI_PIPE_NAME_ROAD = t2.DRAI_PIPE_NAME_ROAD AND
                      t0.DRAI_PIPE_BROAD_NAME = t2.DRAI_PIPE_BROAD_NAME AND t0.DRAI_PIPE_EROAD_NAME = t2.DRAI_PIPE_EROAD_NAME LEFT OUTER JOIN
                          (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME, SUM(DRAI_PIPE_LENGTH)
                                                   AS w3
                            FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_4
                            WHERE      (DRAI_PIPE_D1 >= 1050) AND (DRAI_PIPE_D1 <= 1400)
                            GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                            ORDER BY DRAI_PIPE_NAME_ROAD) AS t3 ON t0.DRAI_PIPE_NAME_ROAD = t3.DRAI_PIPE_NAME_ROAD AND
                      t0.DRAI_PIPE_BROAD_NAME = t3.DRAI_PIPE_BROAD_NAME AND t0.DRAI_PIPE_EROAD_NAME = t3.DRAI_PIPE_EROAD_NAME LEFT OUTER JOIN
                          (SELECT     TOP (100) PERCENT DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME, SUM(DRAI_PIPE_LENGTH)
                                                   AS w4
                            FROM          sde.TDRAI_PIPE_ST AS TDRAI_PIPE_ST_3
                            WHERE      (DRAI_PIPE_D1 >= 1500)
                            GROUP BY DRAI_PIPE_NAME_ROAD, DRAI_PIPE_BROAD_NAME, DRAI_PIPE_EROAD_NAME
                            ORDER BY DRAI_PIPE_NAME_ROAD) AS t4 ON t0.DRAI_PIPE_NAME_ROAD = t4.DRAI_PIPE_NAME_ROAD AND
                      t0.DRAI_PIPE_BROAD_NAME = t4.DRAI_PIPE_BROAD_NAME AND t0.DRAI_PIPE_EROAD_NAME = t4.DRAI_PIPE_EROAD_NAME

這樣就可以了！

在網上找來找去找到這樣的示例：

記錄相加則得到的值爲NULL。下面分析以下我下面的SQL語句

 1select xmno,(select xmbm from xmb where no=a.xmno) as xmbm,
 2(select xmmc from xmb where no=a.xmno) as xmmc,(select jdmc from jdb where jdb.jddm=(select jddm from xmb where no=a.xmno)) as jdmc,(select sj1 from xmb where no=a.xmno) as sj1,
 3(select sj2 from xmb where no=a.xmno) as sj2,
 4(sum(f011+f012+f013+f014+f021+f022+f023+f024+f031+f032+f033+f034+f041+f042+f043+f044+f051+f052+f053+f054+f061+f062+f063+f064+f071+f072+f073+f074+f081+f082+f083+f084+f091+f092+f093+f094+f101+f102+f103+f104+f111+f112+f113+f114+f121+f122+f123+f124)+
 5(select sum(f011+f012+f013+f014+f021+f022+f023+f024+f031+f032+f033+f034+f041+f042+f043+f044+f051+f052+f053+f054+f061+f062+f063+f064+f071+f072+f073+f074+f081+f082+f083+f084+f091+f092+f093+f094+f101+f102+f103+f104+f111+f112+f113+f114+f121+f122+f123+f124)  from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as total,
 6(sum(f011+f021+f031+f041+f051+f061+f071+f081+f091+f101+f111+f121)+(select sum(f011+f021+f031+f041+f051+f061+f071+f081+f091+f101+f111+f121)  from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as zcgs,
 7(sum(f012+f022+f032+f042+f052+f062+f072+f082+f092+f102+f112+f122)+(select sum(f012+f022+f032+f042+f052+f062+f072+f082+f092+f102+f112+f122) from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as jbgs,
 8(sum(f013+f023+f033+f043+f053+f063+f073+f083+f093+f103+f113+f123)+(select sum(f013+f023+f033+f043+f053+f063+f073+f083+f093+f103+f113+f123) from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as wygs,
 9(sum(f014+f024+f034+f044+f054+f064+f074+f084+f094+f104+f114+f124)+(select sum(f014+f024+f034+f044+f054+f064+f074+f084+f094+f104+f114+f124) from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as ccgs 
10from rytj2006 a group by xmno

得到的查詢結果如下


可以看到中間xmno=111的全部爲null值,但是當我從數據庫中單獨查詢數據庫rytj2006中xmno=111的記錄時,發現它是有值存在的，然後我又查詢了相應的lsgRytj2006中xmno=111的記錄結果發現沒有這條記錄，用sum統計出來的數據爲NULL值，原因就出來了，NULL值和數值相加，結果爲NULL值，但是怎麼解決這個問題呢?
馬上想到了cast語句，看能否把NULL值轉換成FLOAT,結果不行，最後用CASE函數來轉換它成功了,以下爲成功的SQL語句。

1select xmno,(select xmbm from xmb where no=a.xmno) as xmbm,
2(select xmmc from xmb where no=a.xmno) as xmmc,(select jdmc from jdb where jdb.jddm=(select jddm from xmb where no=a.xmno)) as jdmc,(select sj1 from xmb where no=a.xmno) as sj1,
3(select sj2 from xmb where no=a.xmno) as sj2,
4(sum(f011+f012+f013+f014+f021+f022+f023+f024+f031+f032+f033+f034+f041+f042+f043+f044+f051+f052+f053+f054+f061+f062+f063+f064+f071+f072+f073+f074+f081+f082+f083+f084+f091+f092+f093+f094+f101+f102+f103+f104+f111+f112+f113+f114+f121+f122+f123+f124) +
5(select case when sum(f011+f012+f013+f014+f021+f022+f023+f024+f031+f032+f033+f034+f041+f042+f043+f044+f051+f052+f053+f054+f061+f062+f063+f064+f071+f072+f073+f074+f081+f082+f083+f084+f091+f092+f093+f094+f101+f102+f103+f104+f111+f112+f113+f114+f121+f122+f123+f124) is null then 0.0 else sum(f011+f012+f013+f014+f021+f022+f023+f024+f031+f032+f033+f034+f041+f042+f043+f044+f051+f052+f053+f054+f061+f062+f063+f064+f071+f072+f073+f074+f081+f082+f083+f084+f091+f092+f093+f094+f101+f102+f103+f104+f111+f112+f113+f114+f121+f122+f123+f124) end from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as total,
6(sum(f011+f021+f031+f041+f051+f061+f071+f081+f091+f101+f111+f121)+(select case when sum(f011+f021+f031+f041+f051+f061+f071+f081+f091+f101+f111+f121) is null then 0.0 else sum(f011+f021+f031+f041+f051+f061+f071+f081+f091+f101+f111+f121) end from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as zcgs,
7(sum(f012+f022+f032+f042+f052+f062+f072+f082+f092+f102+f112+f122)+(select case when sum(f012+f022+f032+f042+f052+f062+f072+f082+f092+f102+f112+f122) is null then 0.0 else sum(f012+f022+f032+f042+f052+f062+f072+f082+f092+f102+f112+f122) end from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as jbgs,
8(sum(f013+f023+f033+f043+f053+f063+f073+f083+f093+f103+f113+f123)+(select case when sum(f013+f023+f033+f043+f053+f063+f073+f083+f093+f103+f113+f123) is null then 0.0 else sum(f013+f023+f033+f043+f053+f063+f073+f083+f093+f103+f113+f123) end from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as wygs,
9(sum(f014+f024+f034+f044+f054+f064+f074+f084+f094+f104+f114+f124)+(select case when sum(f014+f024+f034+f044+f054+f064+f074+f084+f094+f104+f114+f124) is null then 0.0 else sum(f014+f024+f034+f044+f054+f064+f074+f084+f094+f104+f114+f124) end from lsgRytj2006 where lsgRytj2006.xmno=a.xmno)) as ccgs from rytj2006 a group by xmno


得到的最後結果爲:


注意上面的CASE一定要帶上ElSE，否則當查詢統計的結果不爲NULL值，這樣寫後得出的反而爲NULL值.
CASE有兩種寫法，下面摘錄下SQL2000SERVER的幫助文檔,我們上面用到的是第二種,注意後面的例子！

備註：上面自己做的例子是SQL2005數據庫！


CASE

計算條件列表並返回多個可能結果表達式之一。

CASE 具有兩種格式：

  • 簡單 CASE 函數將某個表達式與一組簡單表達式進行比較以確定結果。

  • CASE 搜索函數計算一組布爾表達式以確定結果。

兩種格式都支持可選的 ELSE 參數。

語法

簡單 CASE 函數：

CASE input_expression
    WHEN when_expression THEN result_expression
        [ ...n ]
    [
        ELSE else_result_expression
    END

CASE 搜索函數：

CASE
    WHEN Boolean_expression THEN result_expression
        [ ...n ]
    [
        ELSE else_result_expression
    END

參數

input_expression

是使用簡單 CASE 格式時所計算的表達式。Input_expression 是任何有效的 Microsoft® SQL Server™ 表達式。

WHEN when_expression

使用簡單 CASE 格式時 input_expression 所比較的簡單表達式。When_expression 是任意有效的 SQL Server 表達式。Input_expression 和每個 when_expression 的數據類型必須相同，或者是隱性轉換。

n

佔位符，表明可以使用多個 WHEN when_expression THEN result_expression 子句或 WHEN Boolean_expression THEN result_expression 子句。

THEN result_expression

當 input_expression = when_expression 取值爲 TRUE，或者 Boolean_expression 取值爲 TRUE 時返回的表達式。result expression 是任意有效的 SQL Server 表達式。

ELSE else_result_expression

當比較運算取值不爲 TRUE 時返回的表達式。如果省略此參數並且比較運算取值不爲 TRUE，CASE 將返回 NULL 值。Else_result_expression 是任意有效的 SQL Server 表達式。Else_result_expression 和所有 result_expression 的數據類型必須相同，或者必須是隱性轉換。

WHEN Boolean_expression

使用 CASE 搜索格式時所計算的布爾表達式。Boolean_expression 是任意有效的布爾表達式。

結果類型

從 result_expressions 和可選 else_result_expression 的類型集合中返回最高的優先規則類型。有關更多信息，請參見數據類型的優先順序。

結果值
簡單 CASE 函數：
  • 計算 input_expression，然後按指定順序對每個 WHEN 子句的 input_expression = when_expression 進行計算。

  • 返回第一個取值爲 TRUE 的 (input_expression = when_expression) 的 result_expression。

  • 如果沒有取值爲 TRUE 的 input_expression = when_expression，則當指定 ELSE 子句時 SQL Server 將返回 else_result_expression；若沒有指定 ELSE 子句，則返回 NULL 值。
CASE 搜索函數：
  • 按指定順序爲每個 WHEN 子句的 Boolean_expression 求值。

  • 返回第一個取值爲 TRUE 的 Boolean_expression 的 result_expression。

  • 如果沒有取值爲 TRUE 的 Boolean_expression，則當指定 ELSE 子句時 SQL Server 將返回 else_result_expression；若沒有指定 ELSE 子句，則返回 NULL 值。
示例
A. 使用帶有簡單 CASE 函數的 SELECT 語句

在 SELECT 語句中，簡單 CASE 函數僅檢查是否相等，而不進行其它比較。下面的示例使用 CASE 函數更改圖書分類顯示，以使其更易於理解。

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

下面是結果集：

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. 使用帶有簡單 CASE 函數和 CASE 搜索函數的 SELECT 語句

在 SELECT 語句中，CASE 搜索函數允許根據比較值在結果集內對值進行替換。下面的示例根據圖書的價格範圍將價格（money 列）顯示爲文本註釋。

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

下面是結果集：

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. 使用帶有 SUBSTRING 和 SELECT 的 CASE 函數

下面的示例使用 CASE 和 THEN 生成一個有關作者、圖書標識號和每個作者所著圖書類型的列表。 

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

下面是結果集：

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)

 

終於解決問題了！

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