From 7e68db881d61c88c93555dac1449f66080eca068 Mon Sep 17 00:00:00 2001
From: Aspen Smith <aspen@readyset.io>
Date: Tue, 17 Oct 2023 12:21:01 -0400
Subject: [PATCH] mir: Compile local preds in LEFT JOINs as filters

If we've classified any predicates in a LeftJoin edge in the query graph
as local to either the right parent or the left parent, compile those
predicates as filter nodes above that left parent or right parent.

Release-Note-Core: ReadySet now supports queries which have non
  equi-join-key filters in left joins, as long as those filters mention
  columns from only one side of the join
Change-Id: I71182c8b0290437b3145146d4645085d023b8a58
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/6225
Tested-by: Buildkite CI
Reviewed-by: Luke Osborne <luke@readyset.io>
---
 logictests/weird_joins.test                   | 12 ++++
 .../src/controller/sql/mir/join.rs            | 65 +++++++++++++------
 2 files changed, 57 insertions(+), 20 deletions(-)

diff --git a/logictests/weird_joins.test b/logictests/weird_joins.test
index 07039c1efb..a020e9bf5e 100644
--- a/logictests/weird_joins.test
+++ b/logictests/weird_joins.test
@@ -79,3 +79,15 @@ ON t1.x = t2.x
 AND t2.y = 2
 ----
 1
+
+query II nosort
+SELECT t1.x, t2.y
+FROM t1
+LEFT OUTER JOIN t2
+ON t2.y = 2
+AND t1.x = t2.x
+----
+1
+2
+2
+NULL
diff --git a/readyset-server/src/controller/sql/mir/join.rs b/readyset-server/src/controller/sql/mir/join.rs
index b0cd199a3b..4a1b9de578 100644
--- a/readyset-server/src/controller/sql/mir/join.rs
+++ b/readyset-server/src/controller/sql/mir/join.rs
@@ -45,25 +45,30 @@ pub(super) fn make_joins(
     let mut join_chains = Vec::new();
 
     for jref in qg.join_order.iter() {
-        let (mut join_kind, jps) = match &qg.edges[&(jref.src.clone(), jref.dst.clone())] {
-            QueryGraphEdge::Join { on } => (JoinKind::Inner, on),
-            QueryGraphEdge::LeftJoin {
-                on,
-                left_local_preds,
-                right_local_preds,
-                global_preds,
-                params,
-            } => {
-                if !(left_local_preds.is_empty()
-                    && right_local_preds.is_empty()
-                    && global_preds.is_empty()
-                    && params.is_empty())
-                {
-                    unsupported!("Non equal-join predicates not (yet) supported in left joins");
+        let (mut join_kind, jps, left_preds, right_preds) =
+            match &qg.edges[&(jref.src.clone(), jref.dst.clone())] {
+                QueryGraphEdge::Join { on } => (JoinKind::Inner, on, None, None),
+                QueryGraphEdge::LeftJoin {
+                    on,
+                    left_local_preds,
+                    right_local_preds,
+                    global_preds,
+                    params,
+                } => {
+                    if !global_preds.is_empty() {
+                        unsupported!("Global predicates not yet supported in left joins");
+                    }
+                    if !params.is_empty() {
+                        unsupported!("Parameters not yet supported in left joins");
+                    }
+                    (
+                        JoinKind::Left,
+                        on,
+                        Some(left_local_preds),
+                        Some(right_local_preds),
+                    )
                 }
-                (JoinKind::Left, on)
-            }
-        };
+            };
 
         let (left_chain, right_chain) =
             pick_join_chains(&jref.src, &jref.dst, &mut join_chains, node_for_rel)?;
@@ -80,12 +85,32 @@ pub(super) fn make_joins(
             }
         }
 
+        let mut left_parent = left_chain.last_node;
+        for (i, p) in left_preds.into_iter().flatten().enumerate() {
+            left_parent = mir_converter.make_predicate_nodes(
+                query_name,
+                mir_converter.generate_label(&format!("left_local_{i}").into()),
+                left_parent,
+                p,
+            )?;
+        }
+
+        let mut right_parent = right_chain.last_node;
+        for (i, p) in right_preds.into_iter().flatten().enumerate() {
+            right_parent = mir_converter.make_predicate_nodes(
+                query_name,
+                mir_converter.generate_label(&format!("right_local_{i}").into()),
+                right_parent,
+                p,
+            )?;
+        }
+
         let jn = mir_converter.make_join_node(
             query_name,
             mir_converter.generate_label(&name),
             jps,
-            left_chain.last_node,
-            right_chain.last_node,
+            left_parent,
+            right_parent,
             join_kind,
         )?;