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Join Date: Nov 2007
Location: Bangalore, India
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Oh, btw, if you have any duplicate rows, *I dont think it is possible to delete only the duplicate rows. You have to manually (
) delete them. *
Edit: The only way i can think of is, create a dummy table(new_table). Copy distinct rows from old_table to new_table. Truncate old_table. Copy the records from new_table to old_table. I cant think of ANY query to delete duplicate records from a table.
) delete them. *Edit: The only way i can think of is, create a dummy table(new_table). Copy distinct rows from old_table to new_table. Truncate old_table. Copy the records from new_table to old_table. I cant think of ANY query to delete duplicate records from a table.
Last edited by nav33n : Dec 11th, 2007 at 7:27 am. Reason: Added more..
Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.
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Join Date: Nov 2007
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Originally Posted by techna 
To avoid duplication in column(s) we can create it with unique costraint. Constraint is nothing but rules that you can impose on the columns to be unique or not null etc. To create a unique column you can have the codes like:
create table mytable(col1 datatype unique, col2 datatype,...)
Or declare it as a primary key. Primary key is a combination of both "not null" and "unique" constraints.
Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.
*PM asking for help will be ignored*
*PM asking for help will be ignored*
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Join Date: Aug 2007
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Newbie Poster
Re: SQL - questions . Hi am zeal,
Can anybody please explain to me what GROUP BY in SQL really does?
Can anybody please explain to me what GROUP BY in SQL really does?
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Join Date: Nov 2007
Location: Bangalore, India
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For aggregate functions like SUM, AVG, MIN, MAX etc, you should use group by clause. Group by clause groups the records depending upon the table field you mention. Say, for eg, you have a table. This table has 2 columns, student_marks and subject. You want to know the average marks of each subject. You can do this using the group by clause.
This will calculate the average marks of each subject and shows the average marks for each subject.
Cheers,
Nav
select avg(student_marks) from table group by subjectThis will calculate the average marks of each subject and shows the average marks for each subject.
Cheers,
Nav
Last edited by nav33n : Dec 18th, 2007 at 7:16 am.
Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.
*PM asking for help will be ignored*
*PM asking for help will be ignored*
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