From 67578a7602a5be7eb51f324086c8d49bcf8b7498 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Fri, 16 Jun 2023 11:41:18 +0200
Subject: Merging upstream version 16.2.1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 sqlglot/optimizer/optimize_joins.py | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

(limited to 'sqlglot/optimizer/optimize_joins.py')

diff --git a/sqlglot/optimizer/optimize_joins.py b/sqlglot/optimizer/optimize_joins.py
index 4e0c3a1..d51276f 100644
--- a/sqlglot/optimizer/optimize_joins.py
+++ b/sqlglot/optimizer/optimize_joins.py
@@ -1,3 +1,7 @@
+from __future__ import annotations
+
+import typing as t
+
 from sqlglot import exp
 from sqlglot.helper import tsort
 
@@ -13,25 +17,28 @@ def optimize_joins(expression):
         >>> optimize_joins(parse_one("SELECT * FROM x CROSS JOIN y JOIN z ON x.a = z.a AND y.a = z.a")).sql()
         'SELECT * FROM x JOIN z ON x.a = z.a AND TRUE JOIN y ON y.a = z.a'
     """
+
     for select in expression.find_all(exp.Select):
         references = {}
         cross_joins = []
 
         for join in select.args.get("joins", []):
-            name = join.this.alias_or_name
-            tables = other_table_names(join, name)
+            tables = other_table_names(join)
 
             if tables:
                 for table in tables:
                     references[table] = references.get(table, []) + [join]
             else:
-                cross_joins.append((name, join))
+                cross_joins.append((join.alias_or_name, join))
 
         for name, join in cross_joins:
             for dep in references.get(name, []):
                 on = dep.args["on"]
 
                 if isinstance(on, exp.Connector):
+                    if len(other_table_names(dep)) < 2:
+                        continue
+
                     for predicate in on.flatten():
                         if name in exp.column_table_names(predicate):
                             predicate.replace(exp.true())
@@ -47,17 +54,12 @@ def reorder_joins(expression):
     Reorder joins by topological sort order based on predicate references.
     """
     for from_ in expression.find_all(exp.From):
-        head = from_.this
         parent = from_.parent
-        joins = {join.this.alias_or_name: join for join in parent.args.get("joins", [])}
-        dag = {head.alias_or_name: []}
-
-        for name, join in joins.items():
-            dag[name] = other_table_names(join, name)
-
+        joins = {join.alias_or_name: join for join in parent.args.get("joins", [])}
+        dag = {name: other_table_names(join) for name, join in joins.items()}
         parent.set(
             "joins",
-            [joins[name] for name in tsort(dag) if name != head.alias_or_name],
+            [joins[name] for name in tsort(dag) if name != from_.alias_or_name],
         )
     return expression
 
@@ -75,9 +77,6 @@ def normalize(expression):
     return expression
 
 
-def other_table_names(join, exclude):
-    return [
-        name
-        for name in (exp.column_table_names(join.args.get("on") or exp.true()))
-        if name != exclude
-    ]
+def other_table_names(join: exp.Join) -> t.Set[str]:
+    on = join.args.get("on")
+    return exp.column_table_names(on, join.alias_or_name) if on else set()
-- 
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