sql - Implementing Merge Join in Python -

i familiar join operations in sql, don't understand how work internally.

i given task of implementing merge_join function in python. implemented nested loop join correctly:

def nested_loop_join(self, outer, outer_join_index, inner, inner_join_index):     inner_list = list(inner)     outer_row in outer:         inner_row in inner_list:             if outer_row[outer_join_index] == inner_row[inner_join_index]:                 yield outer_row + inner_row 

my merge join is:

def merge_join(self, outer, outer_join_index, inner, inner_join_index):     inner_list = list(inner)     outer_row in outer:         inner_row in inner_list:             if outer_row[outer_join_index]==inner_row[inner_join_index]:                 yield outer_row+inner_row             else:                 yield outer_row 

but doesn't seem working. understand shouldn't merge join attaching inner table outer? did wrong here?

presumably, referring algorithm called merge join , not sql command called merge (the latter both inserts , updates).

the merge join algorithm takes 2 sorted lists of records. when keys same, produces cartesian product of values 2 records. if either input has key values not in other, key not in output.

i'm not going write python code this. however, if understand algorithm does, should pretty simple convert python.