Add readme

Author: Jose Alberto Calvo Vargas

alter_default_value_in_column/README.md

@@ -0,0 +1,20 @@
+# Tinybird Versions - Alter DEFAULT value in a column of the landing Data Source
+
+[Pull Request](https://github.com/tinybirdco/use-case-examples/pull/338/files)
+
+- Just a add the default values to the desired columns. If the event is not sending the value or it is null, the default value will be applied.
+
+
+```diff
+SCHEMA >
++    `timestamp` DateTime `json:$.timestamp` DEFAULT now(),
++    `session_id` String `json:$.session_id` DEFAULT '',
++    `action` LowCardinality(String) `json:$.action` DEFAULT 'None',
++    `version` LowCardinality(String) `json:$.version` DEFAULT '1.0',
++    `payload` String `json:$.payload` DEFAULT '{}',
+-    `timestamp` DateTime `json:$.timestamp`,
+-    `session_id` String `json:$.session_id`,
+-    `action` LowCardinality(String) `json:$.action`,
+-    `version` LowCardinality(String) `json:$.version`,
+-    `payload` String `json:$.payload`
+```