CASE表达评估问题

Question

I have a SQL query which computes CourseType based on Description as below.

   SELECT    sc.EXSJ_Description,
   sn.STEN_Student_ID , s.STUD_Forename_1, s.STUD_Surname, 
    CASE 
    WHEN sc.EXSJ_Description IN ('FUNCTIONAL SKILLS - ENGLISH (LEVEL 1 & LEVEL  2)',
    'ENGLISH (ENTRY LEVEL)', 'FUNCTIONAL SKILLS ENGLISH') THEN 'Overall'
    WHEN sc.EXSJ_Description IN ('READING -ENGLISH LEVEL 2', 'READING- ENGLISH (LEVEL 1 )', 
    'E2  ENGLISH FUNTIONAL SKILLS READING', 'E2 FUNCTIONAL SKILLS READING', 
    'E3 ENGLISH FUNTIONAL SKILLS READING')THEN 'Reading' 
    WHEN sc.EXSJ_Description IN  ('WRITING- ENGLISH (LEVEL 1 )', 'WRITING- ENGLISH LEVEL  2', 
    'E2 ENGLISH FUNCTIONAL SKILLS WRITING', 'E3 ENGLISH FUNCTIONAL SKILLS WRITING') 
    THEN 'Writing' 
    WHEN sc.EXSJ_Description IN ('SPEAKING & LISTENING- 
ENGLISH LEVEL 2', 'SPEAKING & LISTENING- ENGLISH (LEVEL 1)',
    'E3 ENGLISH FUNCTIONAL SKILLS SPEAKING AND LISTENING', 
'E2 ENGLISH FUNCTIONAL SKILLS SPEAKING AND LISTENING') 
    THEN 'Speaking & Listening' 
    END AS CourseType,
    CASE WHEN e.EXSS_Act_Grade = 'PA' THEN 'Pass' 
    WHEN e.EXSS_Act_Grade = 'FL' THEN 'Fail' 
    WHEN e.EXSS_Act_Grade = 'X' THEN 'Not Attended' END AS Grade
    FROM         
    sql10.NG.dbo.STEN AS sn
LEFT OUTER JOIN sql10.NG.dbo.EXSSexmstsbj AS e 
    ON e.EXSS_Student_ID = sn.STEN_Student_ID 
    AND sn.STEN_Provision_Code = e.EXSS_Provision_Code 
    AND sn.STEN_Provision_Instance = e.EXSS_Provision_Instance
INNER JOIN sql10.NG.dbo.STUDstudent AS s 
    ON s.STUD_Student_ID = sn.STEN_Student_ID
    INNER JOIN sql10.NG.dbo.EXSJexsubject AS sc 
    ON sc.EXSJ_Subject_Code = e.EXSS_Subject_Code
WHERE (e.EXSS_Year = '2015') 
    AND (sn.STEN_Year = '2015') 
    AND (e.EXSS_Awarding_Body IN ('13', '73')) 
    AND (e.EXSS_Provision_Code LIKE 'MA27%') 
    AND (sn.STEN_Provision_Code LIKE '27%') OR
    (sn.STEN_Provision_Code LIKE 'MA27%') 
    AND (sc.EXSJ_Description LIKE '%englis%')
    GO

So there should be 3 Course Types - Overall, Reading or Writing but when I execute the query I see some NULL values which is not expected.

Sample data:

 CREATE TABLE [dbo].[STEN]( [STEN_ISN] [int] IDENTITY(1,1) NOT NULL, [STEN_Student_ID] [char](12) NOT NULL, [STEN_Year] [smallint] NOT NULL, [STEN_Provision_Code] [char](20) NOT NULL, [STEN_Provision_Instance] [char](6) NOT NULL) INSERT INTO [dbo].[STEN]( VALUES ('13068629', '2015', '27107', '151601'), ('14072552 ', '2015', '27107', '151601'), ('14073353', '2015', '27107', '151601'), ('14073645', '2015', '27107/DR01', '151601'), ('15075375', '2015', '27107/DR01', '151601')) 

 CREATE TABLE [dbo].[EXSSexmstsbj]( [EXSS_Year] [smallint] NOT NULL, [EXSS_Student_ID] [char](12) NOT NULL, [EXSS_Act_Grade] [char](6) NOT NULL, [EXSS_Awarding_Body] [char](16) NOT NULL, [EXSS_Provision_Code] [char] (20) NULL, [EXSS_Provision_Intance] [char] (6) NULL)) INSERT INTO dbo.EXSSexmstsbj VALUES ( 2015, '09054118','PA, '13', 'MA27031/A01', '151601'), ( 2015, '1261589','PA, '13', 'MA27031/A01', '151601'), ( 2015, '1364766','FL, '13', 'MA27031/A01', '151601'), ( 2015, '1365244','FL, '13', 'MA27031/A01', '151601'), ( 2015, '1260791','X, '13', 'MA27031/A01', '151601'), 

 CREATE TABLE [dbo].[PRPIProvisionInstance]( [PRPI_ISN] [int] IDENTITY(1,1) NOT NULL, [PRPI_Code] [char](20) NOT NULL, [PRPI_Instance] [char](6) NOT NULL) INSERT INTO [dbo].[PRPIProvisionInstance] VALUES ('19235','27107','151601'), ('19236','27107/DR01','151601'), ('19285','27113', '151601'), ('19286','27113/DR01','151601'), ('19237','27120','151601') 

 CREATE TABLE [dbo].[PRPHProvisionHeader]( [PRPH_Code] [char](20) NOT NULL, [PRPH_Title] [varchar](100) NOT NULL, [PRPH_ML2] [char](6) NOT NULL) INSERT INTO [dbo].[PRPHProvisionHeader]VALUES('27000', 'FS workshop for Art', 'A+D '), (27000/A01','FS workshop for Art','A+D '), ('27031/A01','FS English L2 (MA) (Pearson)',' WFD '), ('27032/A01','FS Maths L2 (MA) (Pearson)',' WFD ') , ('27100/E91','EDEX English E1 FS Sept Start (13195) Tue 6.00-9.00',' PLW ') 

 CREATE TABLE [dbo].[STUDstudent]( [STUD_Student_ID] [char](12) NOT NULL, [STUD_Surname] [varchar](30) NOT NULL, [STUD_Forename_1] [varchar](20) NOT NULL, ) INSERT INTO [dbo].[STUDstudent] ('703666V', 'Aakel','Gail'), ('472833M','Abbott','Emma'), ('481691M','Abbasi','Anisa'), '13072746','Ababio','Anita'), '13070877','Aaronson', 'Fay') 

 CREATE TABLE [dbo].[EXSJexsubject]( [EXSJ_Description] [varchar](100) NOT NULL, [EXSJ_Awarding_Body] [char](16) NOT NULL, ) INSERT INTO [dbo].[EXSJexsubject] VALUES ('E1 ENGLISH FUNCTIONAL SKILLS SPEAKING AND LISTENING', '13'), ('E1 ENGLISH FUNTIONAL SKILLS READING',' 13 '), ('E1 ENGLISH FUNCTIONAL SKILLS WRITING',' 13 '), ('E2 ENGLISH FUNCTIONAL SKILLS SPEAKING AND LISTENING','13'), ('E2 ENGLISH FUNTIONAL SKILLS READING',' 13 ') 

 CREATE TABLE [dbo].[GNUCustom]( [GNUC_Type] [char](4) NOT NULL, [GNUC_Entity_ISN] [int] NOT NULL, GNUC_Text_1 [VARCHAR] (100) NOT NULL) INSERT INTO VALUES (PRPI 571 PRPI 7761 PRPI 8292 PRPI 8346 PRPI 8374 ) 

Kindly suggest where am I going wrong.

Thanks, Ar

Answer 1

I would guess that there are some other values within EXSJ_Description column that are not being picked up in your CASE WHEN statements.

Try this command see if it returns any non-null values:

SELECT  
     EXSJ_Description
FROM 
     sql10.NG.dbo.EXSJexsubject
WHERE 
     EXSJ_Description
     NOT IN 
         ('FUNCTIONAL SKILLS - ENGLISH (LEVEL 1 & LEVEL  2)',
         'ENGLISH (ENTRY LEVEL)',
         'FUNCTIONAL SKILLS ENGLISH',
         'WRITING- ENGLISH (LEVEL 1 )',
         'WRITING- ENGLISH LEVEL  2',
         'E2 ENGLISH FUNCTIONAL SKILLS WRITING',
         'E3 ENGLISH FUNCTIONAL SKILLS WRITING',
         'SPEAKING & LISTENING- ENGLISH LEVEL 2',
         'SPEAKING & LISTENING- ENGLISH (LEVEL 1)',
         'E3 ENGLISH FUNCTIONAL SKILLS SPEAKING AND LISTENING',
         'E2 ENGLISH FUNCTIONAL SKILLS SPEAKING AND LISTENING')

If there are, add them to your conditions. In the future, best practice dictates always using an ELSE to catch any unmatched values.

If they are all null, your joins are probably causing a duplication of data that's creating extra null values. Without your data set it's hard to tell for sure.

Answer 2

Although using exact matches may be desirable in some cases, having lists of exact matches offers the opportunity for typos and may cause maintenance problems in the future.

You might consider using pattern matching here to make the code easier to follow:

(CASE WHEN sc.EXSJ_Description LIKE 'FUNCTIONAL%' OR 
           sc.EXSJ_Description LIKE '%ENTRY%'
     THEN 'Overall'
     WHEN sc.EXSJ_Description LIKE '%READING%'
     THEN 'Reading' 
     WHEN sc.EXSJ_Description LIKE '%WRITING%'
     THEN 'Writing' 
     WHEN sc.EXSJ_Description LIKE '%SPEAKING%LISTENING%'
     THEN 'Speaking & Listening' 
     ELSE 'Unknown'
END) AS CourseType,

Admittedly, this will not work for all naming conventions (if a description has both READING and WRITING , then what?). But it does work for your particular set of names and it reduces the opportunities for a typo, which caused your original problem.

Answer 3

Try this, but not good from performance perspective

CASE
    WHEN REPLACE(sc.EXSJ_Description,' ','') IN (
                        REPLACE('FUNCTIONAL SKILLS - ENGLISH (LEVEL 1 & LEVEL  2)',' ',''),
                        REPLACE('ENGLISH (ENTRY LEVEL)',' ',''),
                        REPLACE('FUNCTIONAL SKILLS ENGLISH',' ','')
                    ) THEN 'Overall'
    WHEN REPLACE(sc.EXSJ_Description,' ','') IN (
                       REPLACE('READING -ENGLISH LEVEL 2',' ',''),
                       REPLACE('READING- ENGLISH (LEVEL 1 )',' ',''), 
                       REPLACE('E2  ENGLISH FUNTIONAL SKILLS READING',' ',''),        
                       REPLACE('E2 FUNCTIONAL SKILLS READING',' ','') 
                       REPLACE('E3 ENGLISH FUNTIONAL SKILLS READING',' ','')
                   )THEN 'Reading' 
    WHEN REPLACE(sc.EXSJ_Description,' ','') IN  (
                       REPLACE('WRITING- ENGLISH (LEVEL 1 )',' ',''),
                       REPLACE('WRITING- ENGLISH LEVEL  2',' ',''), 
                       REPLACE('E2 ENGLISH FUNCTIONAL SKILLS WRITING',' ',''), 
                       REPLACE('E3 ENGLISH FUNCTIONAL SKILLS WRITING',' ','')
                   )THEN 'Writing' 
    ...
    ...