# Join Technology (B)

+ `Merge Join`:
  + column that need to be joined are arranged in order. It can be implementation by index scanning or sort. The ordered data of the driving table are read in batches and return after matching the ordered data of the driving table.
  + There is no concurrency, takes up less memory, and the execution time is generally longer than the**Hash Join**. It is suitable for scenario with large tables and small memory that do not require high execution time.
------------------------------------------------------------