4 files changed, 14 insertions, 2 deletions
diff --git a/sqlglot/optimizer/expand_multi_table_selects.py b/sqlglot/optimizer/expand_multi_table_selects.py
index ba562df..86f0c2d 100644
--- a/sqlglot/optimizer/expand_multi_table_selects.py
+++ b/sqlglot/optimizer/expand_multi_table_selects.py
@@ -2,6 +2,14 @@ from sqlglot import exp
 
 
 def expand_multi_table_selects(expression):
+    """
+    Replace multiple FROM expressions with JOINs.
+
+    Example:
+        >>> from sqlglot import parse_one
+        >>> expand_multi_table_selects(parse_one("SELECT * FROM x, y")).sql()
+        'SELECT * FROM x CROSS JOIN y'
+    """
     for from_ in expression.find_all(exp.From):
         parent = from_.parent
 
diff --git a/sqlglot/optimizer/isolate_table_selects.py b/sqlglot/optimizer/isolate_table_selects.py
index 5bd7b30..5d78353 100644
--- a/sqlglot/optimizer/isolate_table_selects.py
+++ b/sqlglot/optimizer/isolate_table_selects.py
@@ -11,7 +11,7 @@ def isolate_table_selects(expression, schema=None):
         if len(scope.selected_sources) == 1:
             continue
 
-        for (_, source) in scope.selected_sources.values():
+        for _, source in scope.selected_sources.values():
             if not isinstance(source, exp.Table) or not schema.column_names(source):
                 continue
 
diff --git a/sqlglot/optimizer/optimize_joins.py b/sqlglot/optimizer/optimize_joins.py
index fd69832..dc5ce44 100644
--- a/sqlglot/optimizer/optimize_joins.py
+++ b/sqlglot/optimizer/optimize_joins.py
@@ -6,6 +6,11 @@ from sqlglot.optimizer.simplify import simplify
 def optimize_joins(expression):
     """
     Removes cross joins if possible and reorder joins based on predicate dependencies.
+
+    Example:
+        >>> from sqlglot import parse_one
+        >>> 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 = {}
diff --git a/sqlglot/optimizer/optimizer.py b/sqlglot/optimizer/optimizer.py
index 5258c2b..766e059 100644
--- a/sqlglot/optimizer/optimizer.py
+++ b/sqlglot/optimizer/optimizer.py
@@ -64,7 +64,6 @@ def optimize(expression, schema=None, db=None, catalog=None, rules=RULES, **kwar
     possible_kwargs = {"db": db, "catalog": catalog, "schema": schema, **kwargs}
     expression = expression.copy()
     for rule in rules:
-
         # Find any additional rule parameters, beyond `expression`
         rule_params = rule.__code__.co_varnames
         rule_kwargs = {