The Bloom filter or hash map is a data structure that represents the distribution of values in a column or set of columns. It may be used in queries that satisfy the following conditions:
An operation in the query reads its entire input before returning a row to later operations. For example, a join of two tables on a single column requires that all the relevant rows be read to establish whether they meet the criterion for the join.
A later operation in the query refers to the rows in the result of the operation. For example, a second join on the same column would use only those rows that satisfy the first join.