--- 

+++ 

@@ -2,12 +2,28 @@

   name demo.orders,
   dialect bigquery,
   audits (unique_values('columns' = (
-    order_id
+    surrogate_key
   )), not_null('columns' = (
-    order_id
+    surrogate_key
   ))),
   grains (order_id)
 )
+import sqlglot.expressions as exp
+def gen_surrogate_key(evaluator, field_list):
+    if not isinstance(field_list, list):
+        field_list = list(field_list)
+    default_null_value = '_sqlmesh_surrogate_key_null_default_'
+    expressions = []
+    for i, field in enumerate(field_list):
+        coalesce_expression = exp.Coalesce(this=exp.cast(expression=exp.
+            Column(this=field), to='TEXT'), expressions=exp.Literal.string(
+            default_null_value))
+        expressions.append(coalesce_expression)
+        if i < len(field_list) - 1:
+            expressions.append(exp.Literal.string('-'))
+    concat_exp = exp.Concat(expressions=expressions)
+    hash_exp = exp.SHA2(this=concat_exp, length=exp.Literal.number(256))
+    return hash_exp
 @DEF(payment_methods, ['credit_card', 'coupon', 'bank_transfer', 'gift_card'])
 WITH orders AS (
   SELECT
@@ -30,6 +46,7 @@

     order_id
 ), final AS (
   SELECT
+    @gen_surrogate_key() AS surrogate_key,
     orders.order_id,
     orders.customer_id,
     orders.order_date,

--- 

+++ 

@@ -12,5 +12,6 @@

   id AS payment_id,
   order_id,
   payment_method,
-  amount / 100 AS amount
+  amount / 100 AS amount,
+  'new_column' AS new_column
 FROM demo.seed_raw_payments