Question

I am new to mysql and was reading about on duplicate key update. The statement we generally write would be something like this

insert into table (col1,col2) values(1,1) on duplicate key update col2=1;

Assuming col1 to be primary.

My understanding of this is statement is that if there is duplicate value in col1 the respective statement updates col2 with 1. My question is why do we use the term “key” in this statement? As it is understood that the statement updates only when there is a primary key violation. Are there any other parameters or function which we can use with duplicate?

Thanks

Answer 1

MySQL updates either if there is a primary or a unique key violation. The manual covers it quite extensively in a separate chapter with examples:

If you specify ON DUPLICATE KEY UPDATE, and a row is inserted that
would cause a duplicate value in a UNIQUE index or PRIMARY KEY, MySQL
performs an UPDATE of the old row.

The term key is used as part of the syntax definition. The term is afaik only available when performing INSERT-statements. If you insert data by any other means (I can only think of LOAD DATA right now), other mechanisms come into place.