CODEWITHSUNDEEP
sqlsqlplus
Abiodun Adeoye
Abiodun Adeoye

Reputation: 1095

Duplicate columns with inner Join

SELECT 
    dealing_record.*
    ,shares.*
    ,transaction_type.*
FROM 
    shares 
    INNER JOIN shares ON shares.share_ID = dealing_record.share_id
    INNER JOIN transaction_type ON transaction_type.transaction_type_id = dealing_record.transaction_type_id;

The above SQL code produces the desired output but with a couple of duplicate columns. Also, with incomplete display of the column headers. When I change the

linesize 100

the headers shows but data displayed overlaps

I have checked through similar questions but I don't seem to get how to solve this.

Upvotes: 21

Views: 90142

Answers (3)

Manohar
Manohar

Reputation: 131

use NATURAL JOIN to avoid duplicate columns which come when you've used INNER JOIN

Let's say you've Customers table and Orders table and both have CustomerID in common

When you execute the following query:

select * from Customers c inner join Orders o on c.customerID = o.customerID;

Then you'll get the column "CustomerID" two times, one from the Customers table and the other from Orders table.

To avoid this, we need to use NATURAL JOIN.

The syntax of NATURAL JOIN is very simple.

select * from Customers NATURAL JOIN Orders;

That's it. You need not insert any condition on which column to join. You'll get the output in such a way that the output table has only one customerID column.

Upvotes: 3

Alberto Solano
Alberto Solano

Reputation: 8227

You have duplicate columns, because, you're asking to the SQL engine for columns that they will show you the same data (with SELECT dealing_record.* and so on) , and then duplicates.

For example, the transaction_type.transaction_type_id column and the dealing_record.transaction_type_id column will have matching rows (otherwise you won't see anything with an INNER JOIN) and you will see those duplicates.

If you want to avoid this problem or, at least, to reduce the risk of having duplicates in your results, improve your query, using only the columns you really need, as @ConradFrix already said. An example would be this:

SELECT 
    dealing_record.Name
    ,shares.ID
    ,shares.Name
    ,transaction_type.Name
    ,transaction_type.ID
FROM 
    shares 
    INNER JOIN shares ON shares.share_ID = dealing_record.share_id
    INNER JOIN transaction_type ON transaction_type.transaction_type_id = dealing_record.transaction_type_id;

Upvotes: 23

wxyz
wxyz

Reputation: 707

Try to join shares with dealing_record, not shares again:

select dealing_record.*,
       shares.*,
       transaction_type.*
FROM shares inner join dealing_record on shares.share_ID = dealing_record.share_id
            inner join transaction_type on transaction_type.transaction_type_id=
dealing_record.transaction_type_id;

Upvotes: 3

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