Explain the example of HDFS multi file join operation in detail

Explain the example of HDFS multi file join operation in detail

Recently, when processing HDFS files, I encountered multiple file join operations, including all join and common left join operations,

Here is a simple example; Two tables are used for left join. The data structure is as follows:

A documents:

a|1b|2|c

B documents:

a|b|1|2|c

That is, the first and second columns in document a correspond to the first and third columns in document B; Similar to the primary key / foreign key of a table in a database

The code is as follows:

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