Re: Union and NULL

[Ramalingam Chelliah]

Hi ,
Today I found some user comment in ALTER TABLE Documentation Page....

http://dev.mysql.com/doc/mysql/en/ALTER_TABLE.html

Check this one out.. ( Third Comment )
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Posted by Radhakrishnan Ayyappanaicker on April 13 2004 2:41am [Delete] [Edit]

while adding primary key constraint on null allowable integer column, mysql assigns default value 0 iff one NULL value exists on that column else alter table will fail with error "Duplicate entry '0' for key 1"

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Note that he has mentioned something like "mysql assigns default value 0 iff one NULL value exists on a Column(Null allowable Integer) made as Primary Key...


Hope this is useful ....


Regards,
Ram.