SQL: Playing with CROSS JOIN

Last Updated on 14 October 2019 by Roberto De Pedrini A type of join that is little used and considered of lower rank than the other joins is the CROSS JOIN. This operation is used to create all possible combinations of each row between two (or more) tables; it is certainly an option to be used with extreme attention to the cardinality of the tables involved. The lines expected from a cross join are given by the product of the rows of the two (or more) tables participating in the join; imagine if by mistake we cross a table of 1,000,000 rows with a table of 2,000,000 rows: the result is a dataset of 2,000,000,000,000 rows. …