count_if (expression)
Someone just posted a problem on a PostgreSQL mailing list. They had several boolean columns, but they wanted to get how many values were true for each column, but in 1 query. There are several ways to do this, but none of which are particularly elegant. Say we have the following table definition: CREATE TABLE subscribers ( subscriber text PRIMARY KEY, news boolean DEFAULT false, sport boolean DEFAULT false, promotions boolean DEFAULT false, horrible_spam boolean DEFAULT false ); INSERT INTO subscribers (subscriber, news, sport, promotions, horrible_spam) VALUES ('person_a', true, false, false, false), ('person_b', true, true, true, false), ('person_c', true, false, true, true), ('person_d', false, false, false, false), ('person_e', true, true, false, false), ('person_f', true, false, true, true), ('person_g', true, false, false, false); Now we want to get a count of how many of each subscription category has...