Hi

I have some fairly simple requirements but I'm not sure how I implement them:

• I have multiple concurrent threads running the same query
• The query supplies a 'string' value - if it exists in the table, the query should return the id of the matching row, if not the query should insert the 'string' value and return the last inserted id
• The 'string' column is (and must be) a text column (it's bigger than varchar 255) so I cannot set it as unique - uniqueness must be enforced through the access mechanism
• The query needs to be in stored procedure format (which doesnt support table locks in MySQL)

How can I guarantee that 'string' is unique? How can I prevent other threads writing to the table after another thread has read it and found no matching 'string' item?

Thanks for any advice..