Add rest of sql.txt to sql.rst

Author: pgulutzan

doc/reference/reference_sql/column_constraint.spec

@@ -0,0 +1,17 @@
+stack (
+  line(
+    choice(
+      None,
+      line(' CONSTRAINT ', 'name')
+    )
+  ),
+  line(
+    choice(
+      line(' PRIMARY ', ' KEY '),
+      line(' NOT NULL '),
+      line(' UNIQUE '),
+      line(' DEFAULT ', 'expression'),
+      line('foreign-key-clause')
+    )
+  )
+)