Mapping with SQL to MapReduce
We can perform most SQL operations in views also. We only need to change the way we visualize data extraction from the database using SQL and think in terms of the map and reduce functions. Here, we will see how to incorporate SQL queries into the MapReduce format.
Select and where conditions
Any fields or attributes selection for a document from a bucket can be performed by adding it to the emitted key or the value of the
map function, which can be used for selection of attributes in the result set or for performing aggregation in the
reduce function. The key generated by the
map() function determines the ability of the view to query the bucket. Whenever you want to select documents based on some attributes of a document, ...