ygf11 commented on code in PR #5156:
URL: https://github.com/apache/arrow-datafusion/pull/5156#discussion_r1102390256
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datafusion/core/src/physical_plan/joins/nested_loop_join.rs:
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@@ -50,9 +50,27 @@ use crate::error::Result;
use crate::execution::context::TaskContext;
use crate::physical_plan::coalesce_batches::concat_batches;
-/// Data of the left side
+/// Data of the inner table side
type JoinLeftData = RecordBatch;
+/// NestedLoopJoinExec executes partitions in parallel.
+/// One input will be collected to a single partition, call it inner-table.
+/// The other side of the input is treated as outer-table, and the output
Partitioning is from it.
+/// Giving an output partition number x, the execution will be:
+///
+/// ```text
+/// for outer-table-batch in outer-table-partition-x
+/// check-join(outer-table-batch, inner-table-data)
+/// ```
+///
+/// One of the inputs will become inner table, and it is decided by the join
type.
+/// Following is the relation table:
+///
+/// ```text
+/// JoinType Distribution
Inner-table
+/// Inner/Left/LeftSemi/LeftAnti (UnspecifiedDistribution, SinglePartition)
right
+/// Right/RightSemi/RightAnti/Full (SinglePartition, UnspecifiedDistribution)
left
+/// ```
Review Comment:
👍
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