The differences between the tJoin and tMap components


Both tJoin and tMap can be used to do a join between different data sources. However, the two components have different characteristics, depending on your business needs. This article explains the differences between tJoin and tMap.



tJoin is a basic pure component used to do a join, including inner join and left outer join, between two data sources. tMap is more powerful in terms of functionality than tJoin, though tMap can be used to perform the same functionality.


Below is a list of the differences between tJoin and tMap:

  1. tMap can have many output links compared to tJoin, which only has main and reject links.
  2. tMap supports writing expressions on the columns while providing the joining condition, whereas tJoin only supports exact matches between the keys.
  3. tMap supports the storage of the look-up data on disk.
  4. tMap allows you to reload the look-up data for each main record.
  5. tMap supports more types of join model, includes unique join, first join, and all join, whereas tJoin only supports unique join. This article (The differences between Unique match, First match and All matches) discusses the differences between the different join models.
  6. tMap allows you to link multiple look-up flows to it, and supports loading multiple look-up flows in parallel. tJoin only accepts one look-up flow.
  7. tMap supports the 'die on error' option.

From the above list of differences, you can see that tMap is a powerful component that can handle more complicated cases compared to tJoin, which is basic. tMap generates more code while compiling, and it may take more space and time to load the data in the memory during the job execution than tJoin. Generally speaking, you should use tJoin if it is able to meet your requirements; otherwise, use tMap.

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