Now when you add a new name to the list, you can Move to the second name on the list, you compare it to the third namenow You know that you won't find any duplicates later in the list. If the second name is not a duplicate of the first, With the first name, Bowman, David and compare it to the second name,ĭutton, Charles. Time you add a new name to the list, you have to compare it to every other nameĪ better solution would be to first sort the list: Bowman, David Dutton, Charles Dutton, Charles Farman, Jerry Floyd, Heywood Grumby, Jonas Hinkley, Roy Manchek, Arthur Morbius, Edward Poole, Frank Stone, Jeremy Wentworth, EuniceĪfter the list is sorted, it's easy to check for duplicatesanyĭuplicate values appear next to each other. This algorithm wouldĬertainly work, but it would turn out to be slow as the list grew longer. The second name in the list and compare Hinkley, Roy to Wentworth,Įunice, then Floyd, Heywood, and so on. In the following list of names: Grumby, Jonas Hinkley, Roy Wentworth, Eunice Floyd, Heywood Bowman, David Dutton, Charles Poole, Frank Morbius, Edward Farman, Jerry Stone, Jeremy Dutton, Charles Manchek, ArthurĪ first attempt might simply start with the first value and look for aĭuplicate later in the list, comparing Grumby, Jonas to Hinkley, Think about how you might design an algorithm to check for duplicate values The values that you enter into the customer_id column are unique. The implicit index is created so that PostgreSQL has a quick way to ensure that What PostgreSQL is trying to tell you here is that even though youĭidn't explicitly ask for one, an index has been created on your behalf. 'customers_customer_id_key' for table 'customers' Message: NOTICE: CREATE TABLE / UNIQUE will create implicit index When you create this table, PostgreSQL will display a rather terse Here is the definition of the customers table that you created in Second, an index provides quick access to data (in certain circumstances). First, an index can be used to guarantee uniqueness.

Most of the tables that you have created so far have no indexes. Learn More Buy Adding Indexes to a Table

Postgresql coalesce null to use index