1 files changed, 48 insertions, 0 deletions
diff --git a/sqlglot/optimizer/canonicalize.py b/sqlglot/optimizer/canonicalize.py
new file mode 100644
index 0000000..9b3d98a
--- /dev/null
+++ b/sqlglot/optimizer/canonicalize.py
@@ -0,0 +1,48 @@
+import itertools
+
+from sqlglot import exp
+
+
+def canonicalize(expression: exp.Expression) -> exp.Expression:
+    """Converts a sql expression into a standard form.
+
+    This method relies on annotate_types because many of the
+    conversions rely on type inference.
+
+    Args:
+        expression: The expression to canonicalize.
+    """
+    exp.replace_children(expression, canonicalize)
+    expression = add_text_to_concat(expression)
+    expression = coerce_type(expression)
+    return expression
+
+
+def add_text_to_concat(node: exp.Expression) -> exp.Expression:
+    if isinstance(node, exp.Add) and node.type in exp.DataType.TEXT_TYPES:
+        node = exp.Concat(this=node.this, expression=node.expression)
+    return node
+
+
+def coerce_type(node: exp.Expression) -> exp.Expression:
+    if isinstance(node, exp.Binary):
+        _coerce_date(node.left, node.right)
+    elif isinstance(node, exp.Between):
+        _coerce_date(node.this, node.args["low"])
+    elif isinstance(node, exp.Extract):
+        if node.expression.type not in exp.DataType.TEMPORAL_TYPES:
+            _replace_cast(node.expression, "datetime")
+    return node
+
+
+def _coerce_date(a: exp.Expression, b: exp.Expression) -> None:
+    for a, b in itertools.permutations([a, b]):
+        if a.type == exp.DataType.Type.DATE and b.type != exp.DataType.Type.DATE:
+            _replace_cast(b, "date")
+
+
+def _replace_cast(node: exp.Expression, to: str) -> None:
+    data_type = exp.DataType.build(to)
+    cast = exp.Cast(this=node.copy(), to=data_type)
+    cast.type = data_type
+    node.replace(cast)