the database table is shown below, the choice can only be 2, school CTDS or school Entity ID.
I've attached the database as an excel table to make it easier for you guys to see
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A primary key must be unique. It must uniquely identify the record in the master table.
As far as which is more appropriate, look to your business domain. Which "identifier" is most often used in the business? That would be the choice of primary key, if you are using natural keys.
If you don't know, or requirements may change, its a good indication that a surrogate key may be a better choice (database generated primary key).
I didn't look closely at the spreadsheet, I'll leave that up to you, but I'll repeat:
1) If there is unique key in that data, then it is a candidate for a primary key, go to step 2.
2) If that key MAY change at some point, then it is NOT a candidate for a primary key, choose another
3) If there is not another, well, create your own
In Oracle, you would use a sequence: create sequence your_id_seq;
You could create an ID column of type INTEGER or NUMBER, and declare it as PRIMARY KEY.
You would insert new values into the table by using the sequence in your insert statement: insert into tab(id, ...) values(your_id_seq.nextval
In SQL Server and other databases, you may use an identity (autoincrement) column.
In Oracle, you can emulate the transparent, autoincrement by adding an INSERT trigger using the sequence.
>>If size of table is not bigger, do not create indexes.
I can only wonder what your reasoning is, and I think this is very bad advice.
In Oracle, there is no practical reason not to create an index. If your only reason is to avoid having an additional segment, even a 5 row table can be created as an Index Organized Table, which means the table itself is the index (a single segment) and there is no penalty. All upside, no downside.
Always create indexes if possible, the optimizer will use them.
If it is true that both the school_CTDS value and the School_EntityID value are unique for each school (and expected to never change) then either one could be used as the primary key. If one of these will be used more often in searches, then the one that is used the most often should be chosen to be the primary key.
If you want the database to help you make sure that all values in the other column are also unique, you could create a unique key on the other column. This will also be useful if the second column is used occasionally for searching.
Oracle allows us to create a primary and/or unique key either when the table is created, or this can be done later as a separate step. This can be done either before or after data is loaded into the table (as long as the data really is unique).
Business Accounts
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by: leakim971Posted on 2009-10-30 at 17:12:09ID: 25707652
Hello kuntilanak,
I would create a new one.
Regards.