Transaction Questions

Hi,

Following on from my last question, I'm attempting to write a function that inserts periods. Periods are either
bookings,available, or unavailable, each stored in a seperate table, and all have start date and end date columns, all
ofwhich inherit a table 'calendar_entries'. 

The function needs to check that there are no overlapping periods, so I need to check all three tables - I need to
prevententries being added in parrell for the duration of the function. My question is - Is it sufficient to LOCK
calendar_entriesIN EXCLUSIVE MODE, or do I need to lock all three tables individually? 

Also, inside the function I need to use a transaction in order to DELETE one row, and UPDATE another. Will this 'inner'
transactionhave write access to all 3 tables? 

Just trying to get my head around concurrency - Have a good weekend!

Ta,

Neil.


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