Materialize/doc/user/content/sql/explain-schema.md

---

title: "EXPLAIN SCHEMA" description: "EXPLAIN KEY SCHEMA or EXPLAIN VALUE SCHEMA is used to see the generated schemas for a CREATE SINK statement" menu: main:

parent: commands

---

EXPLAIN KEY SCHEMA or EXPLAIN VALUE SCHEMA shows the generated schemas for a CREATE SINK statement without creating the sink.

{{< warning >}} EXPLAIN is not part of Materialize's stable interface and is not subject to our backwards compatibility guarantee. The syntax and output of EXPLAIN may change arbitrarily in future versions of Materialize. {{< /warning >}}

Syntax

{{< diagram "explain-schema.svg" >}}

sink_definition

{{< diagram "sink-definition.svg" >}}

Output format

Only JSON can be specified as the output format.

Output type	Description
JSON	Format the explanation output as a JSON object.

Details

When creating a an Avro-formatted Kafka sink, Materialize automatically generates Avro schemas for the message key and value and publishes them to a schema registry. This command shows what the generated schemas would look like, without creating the sink.

Examples

CREATE TABLE t (c1 int, c2 text);
COMMENT ON TABLE t IS 'materialize comment on t';
COMMENT ON COLUMN t.c2 IS 'materialize comment on t.c2';

EXPLAIN VALUE SCHEMA FOR
  CREATE SINK
  FROM t
  INTO KAFKA CONNECTION kafka_conn (TOPIC 'test_avro_topic')
  KEY (c1)
  FORMAT AVRO USING CONFLUENT SCHEMA REGISTRY CONNECTION csr_conn
  ENVELOPE UPSERT;

                   Schema
--------------------------------------------
 {                                         +
   "type": "record",                       +
   "name": "envelope",                     +
   "doc": "materialize comment on t",      +
   "fields": [                             +
     {                                     +
       "name": "c1",                       +
       "type": [                           +
         "null",                           +
         "int"                             +
       ]                                   +
     },                                    +
     {                                     +
       "name": "c2",                       +
       "type": [                           +
         "null",                           +
         "string"                          +
       ],                                  +
       "doc": "materialize comment on t.c2"+
     }                                     +
   ]                                       +
 }

Privileges

The privileges required to execute this statement are:

{{< include-md file="shared-content/sql-command-privileges/explain-schema.md"

}}