docs: data validations (close #4085) (#4260)

CHANGELOG.md

@@ -278,6 +278,7 @@ A new CLI migrations image is introduced to account for the new migrations workf
 (close #3969) (#4145)
 
 ### Bug fixes and improvements
+
 - server: improve performance of replace_metadata tracking many tables (fix #3802)
 - server: option to reload remote schemas in 'reload_metadata' API (fix #3792, #4117)
 - server: fix various space leaks to avoid excessive memory consumption
@@ -361,3 +362,4 @@ Read more about it in the [docs](https://hasura.io/docs/1.0/graphql/manual/auth/
 - server: check expression in update permissions (close #384) (rfc #3750) (#3804)
 - console: show pre-release update notifications with opt out option (#3888)
 - console: handle invalid keys in permission builder (close #3848) (#3863)
+- docs: add page on data validation to docs (close #4085) (#4260)

docs/graphql/manual/schema/computed-fields.rst

@@ -16,8 +16,8 @@ What are computed fields?
 -------------------------
 
 Computed fields are virtual values or objects that are dynamically computed and can be queried along with a table's
-columns. Computed fields are computed when requested for via SQL functions using other columns of the table and other
-custom inputs if needed.
+columns. Computed fields are computed when requested for via `custom SQL functions <https://www.postgresql.org/docs/current/sql-createfunction.html>`__
+using other columns of the table and other custom inputs if needed.
 
 .. note::
 

docs/graphql/manual/schema/custom-functions.rst

@@ -4,8 +4,8 @@
 
 .. _custom_sql_functions:
 
-Customise schema with SQL functions
-===================================
+Extend schema with SQL functions
+================================
 
 .. contents:: Table of contents
   :backlinks: none
@@ -18,15 +18,19 @@ What are custom SQL functions?
 Custom SQL functions are `user-defined SQL functions <https://www.postgresql.org/docs/current/sql-createfunction.html>`_
 that can be used to either encapsulate some custom business logic or extend the built-in SQL functions and operators.
 
-Hasura GraphQL engine lets you expose certain types of custom functions over the GraphQL API to allow querying them
-using both ``queries`` and ``subscriptions``.
+Hasura GraphQL engine lets you expose certain types of custom functions as top level fields in the GraphQL API to allow
+querying them using both ``queries`` and ``subscriptions``.
+
+.. note::
+
+  Custom SQL functions can also be queried as :ref:`computed fields <computed_fields>` of tables.
 
 .. _supported_sql_functions:
 
 Supported SQL functions
------------------------
+***********************
 
-Currently, only functions which satisfy the following constraints can be exposed over the GraphQL API
+Currently, only functions which satisfy the following constraints can be exposed as top level fields in the GraphQL API
 (*terminology from* `Postgres docs <https://www.postgresql.org/docs/current/sql-createfunction.html>`__):
 
 - **Function behaviour**: ONLY ``STABLE`` or ``IMMUTABLE``