1 files changed, 75 insertions, 0 deletions
diff --git a/sqlglot/optimizer/optimize_joins.py b/sqlglot/optimizer/optimize_joins.py
new file mode 100644
index 0000000..40e4ab1
--- /dev/null
+++ b/sqlglot/optimizer/optimize_joins.py
@@ -0,0 +1,75 @@
+from sqlglot import exp
+from sqlglot.helper import tsort
+from sqlglot.optimizer.simplify import simplify
+
+
+def optimize_joins(expression):
+    """
+    Removes cross joins if possible and reorder joins based on predicate dependencies.
+    """
+    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)
+
+            if tables:
+                for table in tables:
+                    references[table] = references.get(table, []) + [join]
+            else:
+                cross_joins.append((name, join))
+
+        for name, join in cross_joins:
+            for dep in references.get(name, []):
+                on = dep.args["on"]
+                on = on.replace(simplify(on))
+
+                if isinstance(on, exp.Connector):
+                    for predicate in on.flatten():
+                        if name in exp.column_table_names(predicate):
+                            predicate.replace(exp.TRUE)
+                            join.on(predicate, copy=False)
+
+    expression = reorder_joins(expression)
+    expression = normalize(expression)
+    return expression
+
+
+def reorder_joins(expression):
+    """
+    Reorder joins by topological sort order based on predicate references.
+    """
+    for from_ in expression.find_all(exp.From):
+        head = from_.expressions[0]
+        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)
+
+        parent.set(
+            "joins",
+            [joins[name] for name in tsort(dag) if name != head.alias_or_name],
+        )
+    return expression
+
+
+def normalize(expression):
+    """
+    Remove INNER and OUTER from joins as they are optional.
+    """
+    for join in expression.find_all(exp.Join):
+        if join.kind != "CROSS":
+            join.set("kind", None)
+    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
+    ]