Added query to find columns of json type. Use jsonb instead.

sql/columns_with_json_type.sql

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2019-2022. Ivan Vakhrushev and others.
+ * https://github.com/mfvanek/pg-index-health-sql
+ *
+ * Licensed under the Apache License 2.0
+ */
+
+-- Finds columns of type 'json'. Use 'jsonb' instead.
+--
+-- See also https://www.postgresql.org/docs/current/datatype-json.html
+-- and https://medium.com/geekculture/postgres-jsonb-usage-and-performance-analysis-cdbd1242a018
+select
+    t.oid::regclass::text as table_name,
+    col.attname::text as column_name,
+    col.attnotnull as column_not_null
+from pg_catalog.pg_class t
+    join pg_catalog.pg_namespace nsp on nsp.oid = t.relnamespace
+    join pg_catalog.pg_attribute col on (col.attrelid = t.oid)
+where
+    t.relkind = 'r' and
+    col.attnum > 0 and /* to filter out system columns such as oid, ctid, xmin, xmax, etc.*/
+    col.atttypid::regtype::text = 'json' and
+    nsp.nspname = :schema_name_param::text
+order by t.oid::regclass::text, col.attname::text;