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Asked: 2026-06-09T22:19:00+00:00

I have a table which is not normalized and I can’t change the structure

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I have a table which is not normalized and I can’t change the structure of the table. The table contains 6 columns to hold preferences namely preference_num1…preference_num6. I want to extract data from table so that it looks like there are 6 rows with one preference being in one row.

To make it clear, the output should be Id,semester_start,year_start,email,preference_num. And, each row would be broken into 6 rows .

Name                    Null     Type          
----------------------- -------- ------------- 
ID                               number (primary key)
YEAR_START                       NUMBER        
SEMESTER_START                   VARCHAR2(8)   
EMAIL                            VARCHAR2(100) 
PREFERENCE_NUM_1                 VARCHAR2(1)   
PREF_INSTITUTION_NAME_1          VARCHAR2(100) 
PREF_INSTITUTION_CODE_1          VARCHAR2(15)  
PREF_COURSE_TITLE_1              VARCHAR2(100) 
COURSE_CODE_1                    VARCHAR2(15)  
OFFERING_LABLE_1                 VARCHAR2(15)  
PREFERENCE_NUM_2                 VARCHAR2(1)   
PREF_INSTITUTION_NAME_2          VARCHAR2(100) 
PREF_INSTITUTION_CODE_2          VARCHAR2(15)  
PREF_COURSE_TITLE_2              VARCHAR2(100) 
COURSE_CODE_2                    VARCHAR2(15)  
OFFERING_LABLE_2                 VARCHAR2(15)  
PREFERENCE_NUM_3                 VARCHAR2(1)   
PREF_INSTITUTION_NAME_3          VARCHAR2(100) 
PREF_INSTITUTION_CODE_3          VARCHAR2(15)  
PREF_COURSE_TITLE_3              VARCHAR2(100) 
COURSE_CODE_3                    VARCHAR2(15)  
OFFERING_LABLE_3                 VARCHAR2(15)  
PREFERENCE_NUM_4                 VARCHAR2(1)   
PREF_INSTITUTION_NAME_4          VARCHAR2(100) 
PREF_INSTITUTION_CODE_4          VARCHAR2(15)  
PREF_COURSE_TITLE_4              VARCHAR2(100) 
COURSE_CODE_4                    VARCHAR2(15)  
OFFERING_LABLE_4                 VARCHAR2(15)  
PREFERENCE_NUM_5                 VARCHAR2(1)   
PREF_INSTITUTION_NAME_5          VARCHAR2(100) 
PREF_INSTITUTION_CODE_5          VARCHAR2(15)  
PREF_COURSE_TITLE_5              VARCHAR2(100) 
COURSE_CODE_5                    VARCHAR2(15)  
OFFERING_LABLE_5                 VARCHAR2(15)  
PREFERENCE_NUM_6                 VARCHAR2(1)   
PREF_INSTITUTION_NAME_6          VARCHAR2(100) 
PREF_INSTITUTION_CODE_6          VARCHAR2(15)  
PREF_COURSE_TITLE_6              VARCHAR2(100) 
COURSE_CODE_6                    VARCHAR2(15)  
OFFERING_LABLE_6                 VARCHAR2(15)  
DATA_EXTRACTION_DATE             DATE          
OFFER_DATE_1                     DATE          
OFFER_RESPONSE_1                 VARCHAR2(20)  
FINAL_OFFER_RESPONSE_1           VARCHAR2(20)  
OFFER_DATE_2                     DATE          
OFFER_RESPONSE_2                 VARCHAR2(20)  
FINAL_OFFER_RESPONSE_2           VARCHAR2(20)  
OFFER_DATE_3                     DATE          
OFFER_RESPONSE_3                 VARCHAR2(20)  
FINAL_OFFER_RESPONSE_3           VARCHAR2(20)  
OFFER_DATE_4                     DATE          
OFFER_RESPONSE_4                 VARCHAR2(20)  
FINAL_OFFER_RESPONSE_4           VARCHAR2(20)  
OFFER_DATE_5                     DATE          
OFFER_RESPONSE_5                 VARCHAR2(20)  
FINAL_OFFER_RESPONSE_5           VARCHAR2(20)  
OFFER_DATE_6                     DATE          
OFFER_RESPONSE_6                 VARCHAR2(20)  
FINAL_OFFER_RESPONSE_6           VARCHAR2(20)

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1 Answer

  1. Editorial Team

    You might find more information about this if you search for UNPIVOT techniques or “oracle columns to rows”.

    One way of doing this is as below, which works well if you are inputting one (indexed) id. I am getting only 3 of the preferences to keep the example simple.

    This is the basic idea.

    select id, sem_start, year_start, pref_num1 from table_1 where id = input_id
union all 
select id, sem_start, year_start, pref_num2 from table_1 where id = input_id
union all
select id, sem_start, year_start, pref_num3 from table_1 where id = input_id

    You should use this query instead, which would be more performant, since we are querying by id only once.

    with t1 as
(select * from table_1 where id = id1)
select id, sem_start, year_start, pref_num1 from t1
union all 
select id, sem_start, year_start, pref_num2 from t1
union all
select id, sem_start, year_start, pref_num3 from t1
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