What's the difference between Primary Key, Unique Key and Index in MySQL?
When should I use KEY, PRIMARY KEY, UNIQUE KEY and INDEX? ...
unique-key
rails relationship using unique key
Hi, I have 2 entities: Table/Entity 1: RetrievedDataRecords Columns: id record_key Table/Entity 2: SourceKeys Columns: id key_name (unique key) I cant alter these tables for legacy reasons, but want rails relationship between RetrievedDataRecord and SourceKey using record_key and key_name (they are the same key) in RetrievedDat...
MySQL Set NULLABLE Unique Field
Hi there, I've a case where I need to store twitter username, email, and some other field to be unique. However, I can only set twitter username later. Not on registration process. How can I handle this in SQL? Here's my current SQL structure: CREATE TABLE `kios_users` ( `id` int(11) NOT NULL AUTO_INCREMENT, `username` varchar(32) NO...
Add new keys to a dictionary while incrementing existing values
I am processing a CSV file and counting the unique values of column 4. So far I have coded this three ways. One uses "if key in dictionary", the second traps the KeyError and the third uses "DefaultDictionary". For example (where x[3] is the value from the file and "a" is a dictionary): First way: if x[3] in a: a[x[3]] += 1 else: ...