Overview
Both of tJoin and tMap can be used to do a join between different data sources, however, the two components have different characteristics, when to use tJoin or tMap, depending on your business needs. This article explains the differences between tJoin and tMap.
Difference
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 as tJoin, but they are different components and are designed for different needs.
Below is the list of the differences between tJoin and tMap:
- tMap can have many output links compared to tJoin which only has a main and reject links.
- tMap supports for writing expression on the columns while providing the joining condition, however, tJoin only supports exact match between the keys.
- tMap supports the storage of the look-up data on disk.
- tMap allows you to reload the look-up data for each main record.
- tMap supports more types of join model, includes unique join, first join and all join, however, tJoin only supports unique join. About the different join models, read this article The differences between Unique match, First match and All matches.
- tMap allows you to link multiple look-up flows to it, and supports to load multiple look-up flows parallel, however, tJoin only accepts one look-up flow.
- tMap supports 'die on error' option.
From the above list of differences, we can see that tMap is quite powerful component compared to tJoin which is basic, it can achieve more complicated cases. As being a powerful component, it 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, we should use tJoin if it is able to meet our requirements otherwise tMap.
