findepi commented on code in PR #13823:
URL: https://github.com/apache/datafusion/pull/13823#discussion_r1889838140
##########
datafusion/common/src/join_type.rs:
##########
@@ -28,21 +28,26 @@ use crate::{DataFusionError, Result};
/// Join type
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Hash)]
pub enum JoinType {
- /// Inner Join
+ /// Inner Join - Returns rows where there is a match in both tables.
Review Comment:
if we want to get precise, this should also say that all matches are
returned (n-to-m)
##########
datafusion/common/src/join_type.rs:
##########
@@ -28,21 +28,26 @@ use crate::{DataFusionError, Result};
/// Join type
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Hash)]
pub enum JoinType {
- /// Inner Join
+ /// Inner Join - Returns rows where there is a match in both tables.
Inner,
- /// Left Join
+ /// Left Join - Returns all rows from the left table and matching rows
from the right table.
+ /// If no match, NULL values are returned for columns from the right table.
Left,
- /// Right Join
+ /// Right Join - Returns all rows from the right table and matching rows
from the left table.
+ /// If no match, NULL values are returned for columns from the left table.
Right,
- /// Full Join
+ /// Full Join - Returns all rows when there is a match in either table.
+ /// Rows without a match in one table will have NULL values for columns
from that table.
Review Comment:
> there is a match in either table
"a match" implies a matching row in left and right tables.
also see above, this should also imply cardinality
maybe
```
/// Full Join - returns all matches between left and right table,
/// plus left table rows without a match (with NULL values for right table
columns)
/// plus right table rows without a match (with NULL values for left table
columns)
```
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