afs commented on code in PR #132:
URL: https://github.com/apache/jena-site/pull/132#discussion_r1030641717
##########
source/documentation/query/lateral-join.md:
##########
@@ -0,0 +1,174 @@
+---
+title: ARQ - Lateral Join
+---
+
+Lateral joins using the keyword `LATERAL` were introduced in Apache jena 4.7.0.
+
+A `LATERAL` join is like a foreach loop, looping on the results from the
+left-hand side (LHS), the pattern before the `LATERAL` keyword, and executing
+the right-hand side (RHS) query pattern once for each row, with the variables
+from the input LHS in-scope during each RHS evaluation.
+
+A regular join only executes the RHS once, and the variables from the LHS are
+used for the join condition after evaluation of the left and right
+sub-patterns.
+
+Another way to think of a lateral join is as a `flatmap`.
+
+Examples:
+```
+## Get exactly one label for each subject with type `:T`
+SELECT * {
+ ?s rdf:type :T
+ LATERAL {
+ SELECT * { ?s rdfs:label ?label } LIMIT 1
+ }
+}
+```
+
+```
+## Get zero or one labels for each subject.
+SELECT * {
+ ?s ?p ?o
+ LATERAL { OPTIONAL { SELECT * ?s rdfs:label ?label } LIMIT 1}
+ }
+}
+```
+
+#### Syntax
+
+The `LATERAL` keyword which takes the graph pattern so far in the group, from
+the `{` starting of the current block, and a `{ }` block afterwards.
+
+#### Evaluation
+
+[Substituting variables](https://afs.github.io/substitute.html) from the LHS
into the RHS (with the same restrictions), then executing the pattern, gives
the evaluation of `LATERAL`
Review Comment:
Eventually!
It is a better/fixed way to do EXISTS and LATERAL but Jena does not
currently have a specific implementation.
It's on my ToDo list.
##########
source/documentation/query/lateral-join.md:
##########
@@ -0,0 +1,174 @@
+---
+title: ARQ - Lateral Join
+---
+
+Lateral joins using the keyword `LATERAL` were introduced in Apache jena 4.7.0.
+
+A `LATERAL` join is like a foreach loop, looping on the results from the
+left-hand side (LHS), the pattern before the `LATERAL` keyword, and executing
+the right-hand side (RHS) query pattern once for each row, with the variables
+from the input LHS in-scope during each RHS evaluation.
+
+A regular join only executes the RHS once, and the variables from the LHS are
+used for the join condition after evaluation of the left and right
+sub-patterns.
+
+Another way to think of a lateral join is as a `flatmap`.
+
+Examples:
+```
+## Get exactly one label for each subject with type `:T`
+SELECT * {
+ ?s rdf:type :T
+ LATERAL {
+ SELECT * { ?s rdfs:label ?label } LIMIT 1
+ }
+}
+```
+
+```
+## Get zero or one labels for each subject.
+SELECT * {
+ ?s ?p ?o
+ LATERAL { OPTIONAL { SELECT * ?s rdfs:label ?label } LIMIT 1}
+ }
+}
+```
+
+#### Syntax
+
+The `LATERAL` keyword which takes the graph pattern so far in the group, from
+the `{` starting of the current block, and a `{ }` block afterwards.
+
+#### Evaluation
+
+[Substituting variables](https://afs.github.io/substitute.html) from the LHS
into the RHS (with the same restrictions), then executing the pattern, gives
the evaluation of `LATERAL`
Review Comment:
Done
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