Hi all,
I'm wanting to add a primary key to a table? I drop the key field and
re-created as

ADD sourceid VARCHAR(4) NOT NULL

then I tried to add

ALTER TABLE SOURCE_ID
ADD PRIMARY KEY (sourceid);

I get this error,

ISC ERROR CODE:335544349
ISC ERROR MESSAGE:
attempt to store duplicate value (visible to active transactions) in unique
index "RDB$PRIMARY5"
null segment of UNIQUE KEY

what am I doing wrong?
Please
Daniel