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Editorial Team
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Asked: 2026-06-17T07:50:21+00:00

I’m trying to add a key from my customer table to my reservation table

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I’m trying to add a key from my customer table to my reservation table in oracle.
However I keep getting an error message when I try to run my SQL commands which states ‘Customer_ID is an invalid identifier’.

What I am trying to do is first use an alter statement to alter the reservation table.
Then I am adding a foreign key, which is called ‘Customer_ID’
Then I enter a references statement, which tells it that I am getting the CUSTOMER_ID attribute from the customer table. However to sql this doesn’t make sense at all.

To me, logically it makes sense, I don’t see anything wrong with the syntax or structure of the statements. Any sharp eyes/minds to help me on this matter would be greatly appreciated.

the statements used are:

ALTER TABLE reservation
ADD FOREIGN KEY (Customer_ID)
REFERENCES Customer(Customer_ID);
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1 Answer

  1. Editorial Team

    There’s nothing wrong with your syntax; I was able to create simple one-column tables with the appropriate names then execute exactly the statement you posted. So I suspect the column CUSTOMER_ID does not exist in one or the other table. Describe the two tables and double-check the column names. Keep in mind that normally column names in Oracle are case-insensitive, but they can be case-sensitive if enclosed in double quotes; this can be a reason for a non-obvious column name mismatch.

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