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Editorial Team
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Asked: 2026-05-20T14:11:22+00:00

I am trying to add a foreign key to a table, and it give

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I am trying to add a foreign key to a table, and it give me the following error:

There are no primary or candidate keys in the referenced table ‘tbl_Person’ that match the referencing column list in the foreign key ‘P_ID’.

I have a tbl_Person, which is defined as:

P_ID INT (Primary Key)
f_Name,
l_Name

the other table is a comments table which is defined as:

C_ID INT,
Comments,
P_ID (should be the foreign key)

Trying to make a one to many relationship table, so when the user add a comment, it is referenced back to him, also, he can add onto the comments without initializing a new comment. Hopefully that makes a little sense.

Ex: Randy Bing enter “I love SQL”, his ID is 1, f_Name is Randy, l_Name is Bing, his comments are “I love Sql”. His comments should store a unique ID, as well as import his P_ID.

Later on when Randy wants to add onto the comment with the same C_ID where P_ID matches him without creating a new C_ID.

Here is the Code:

ALTER TABLE tbl_Comments 
ADD CONSTRAINT P_ID
FOREIGN KEY (P_ID) 
REFERENCES tbl_Person(P_ID)

Am I close to being on the right track?

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1 Answer

  1. Editorial Team

    This error usually means the datatypes are different between “Comments” and “Person”, assuming this is the actual message

    The SQL should be this

    ALTER TABLE tbl_Comments WITH CHECK ADD
 CONSTRAINT FK_Comments_Person FOREIGN KEY (P_ID) REFERENCES tbl_Person (P_ID)

    This matches what you added. So:

    • check datatypes are both int
    • ensure P_ID is primary key on tbl_Person
    • (Edit, Dec 2011) collation and length must be the same for varchar columns too
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