Hash joins

- [Instructor] Another algorithm … for performing joins is the hash join. … Hash joins use a function to map data … into a value that can act as an index into an array. … Hash functions are designed so that the output value … is virtually unique across all of the values in the domain, … where that is the set of possible input values. … Even slight changes to the input value … can lead to different outputs. … Part of the process of hash joining … is building a table of hash values. … The smaller of the two tables is used. … For each key value in the smaller table, … we compute a hash value and store that in the table. … The next step is called the probe phase. … In this step, we calculate the hash value … of each row, and then look up the corresponding value … in the hash table. … The hash table contains a pointer, … or reference to the location of the row we are joining to. … It's important to note that hash joints … only work with equality conditions. … They don't help when you're using …