[SPARK-52710][SQL] DESCRIBE SCHEMA should print collation

### What changes were proposed in this pull request?
Extended `DescribeDatabaseCommand` to print collation.

### Why are the changes needed?
Part of new feature.

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
Updated `describe.sql`.

### Was this patch authored or co-authored using generative AI tooling?
No.

Closes #51401 from ilicmarkodb/fix_describe_schema.

Authored-by: ilicmarkodb <marko.ilic@databricks.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

Author: ilicmarkodb

sql/core/src/main/scala/org/apache/spark/sql/execution/command/ddl.scala

@@ -189,8 +189,9 @@ case class DescribeDatabaseCommand(
       Row("Catalog Name", SESSION_CATALOG_NAME) ::
         Row("Database Name", dbMetadata.name) ::
         Row("Comment", dbMetadata.description) ::
-        Row("Location", CatalogUtils.URIToString(dbMetadata.locationUri))::
-        Row("Owner", allDbProperties.getOrElse(PROP_OWNER, "")) :: Nil
+        Row("Location", CatalogUtils.URIToString(dbMetadata.locationUri)) ::
+        Row("Owner", allDbProperties.getOrElse(PROP_OWNER, "")) ::
+        allDbProperties.get(PROP_COLLATION).map(Row("Collation", _)).toList
 
     if (extended) {
       val properties = allDbProperties -- CatalogV2Util.NAMESPACE_RESERVED_PROPERTIES

sql/core/src/test/resources/sql-tests/analyzer-results/describe.sql.out

@@ -213,6 +213,41 @@ org.apache.spark.sql.catalyst.parser.ParseException
 }
 
 
+-- !query
+DROP SCHEMA IF EXISTS test_schema
+-- !query analysis
+DropNamespace true, false
++- ResolvedNamespace V2SessionCatalog(spark_catalog), [test_schema]
+
+
+-- !query
+CREATE SCHEMA test_schema DEFAULT COLLATION UNICODE
+-- !query analysis
+CreateNamespace false, [collation=UNICODE]
++- ResolvedNamespace V2SessionCatalog(spark_catalog), [test_schema]
+
+
+-- !query
+DESCRIBE SCHEMA EXTENDED test_schema
+-- !query analysis
+DescribeNamespace true, [info_name#x, info_value#x]
++- ResolvedNamespace V2SessionCatalog(spark_catalog), [test_schema]
+
+
+-- !query
+ALTER SCHEMA test_schema DEFAULT COLLATION UTF8_LCASE
+-- !query analysis
+SetNamespaceCollationCommand UTF8_LCASE
++- ResolvedNamespace V2SessionCatalog(spark_catalog), [test_schema]
+
+
+-- !query
+DESCRIBE SCHEMA EXTENDED test_schema
+-- !query analysis
+DescribeNamespace true, [info_name#x, info_value#x]
++- ResolvedNamespace V2SessionCatalog(spark_catalog), [test_schema]
+
+
 -- !query
 DESC temp_v
 -- !query analysis

sql/core/src/test/resources/sql-tests/inputs/describe.sql

@@ -64,6 +64,13 @@ DESC t PARTITION (c='Us');
 -- ParseException: PARTITION specification is incomplete
 DESC t PARTITION (c='Us', d);
 
+-- DESC SCHEMA
+DROP SCHEMA IF EXISTS test_schema;
+CREATE SCHEMA test_schema DEFAULT COLLATION UNICODE;
+DESCRIBE SCHEMA EXTENDED test_schema;
+ALTER SCHEMA test_schema DEFAULT COLLATION UTF8_LCASE;
+DESCRIBE SCHEMA EXTENDED test_schema;
+
 -- DESC Temp View
 
 DESC temp_v;

sql/core/src/test/resources/sql-tests/results/describe.sql.out

@@ -453,6 +453,58 @@ org.apache.spark.sql.catalyst.parser.ParseException
 }
 
 
+-- !query
+DROP SCHEMA IF EXISTS test_schema
+-- !query schema
+struct<>
+-- !query output
+
+
+
+-- !query
+CREATE SCHEMA test_schema DEFAULT COLLATION UNICODE
+-- !query schema
+struct<>
+-- !query output
+
+
+
+-- !query
+DESCRIBE SCHEMA EXTENDED test_schema
+-- !query schema
+struct<info_name:string,info_value:string>
+-- !query output
+Catalog Name	spark_catalog
+Collation	UNICODE
+Comment	
+Location [not included in comparison]/{warehouse_dir}/test_schema.db
+Namespace Name	test_schema
+Owner	[not included in comparison]
+Properties
+
+
+-- !query
+ALTER SCHEMA test_schema DEFAULT COLLATION UTF8_LCASE
+-- !query schema
+struct<>
+-- !query output
+
+
+
+-- !query
+DESCRIBE SCHEMA EXTENDED test_schema
+-- !query schema
+struct<info_name:string,info_value:string>
+-- !query output
+Catalog Name	spark_catalog
+Collation	UTF8_LCASE
+Comment	
+Location [not included in comparison]/{warehouse_dir}/test_schema.db
+Namespace Name	test_schema
+Owner	[not included in comparison]
+Properties
+
+
 -- !query
 DESC temp_v
 -- !query schema

sql/core/src/test/scala/org/apache/spark/sql/SQLQueryTestSuite.scala

@@ -156,6 +156,7 @@ class SQLQueryTestSuite extends QueryTest with SharedSparkSession with SQLHelper
     // SPARK-39564: don't print out serde to avoid introducing complicated and error-prone
     // regex magic.
     .set("spark.test.noSerdeInExplain", "true")
+    .set(SQLConf.SCHEMA_LEVEL_COLLATIONS_ENABLED, true)
 
   // SPARK-32106 Since we add SQL test 'transform.sql' will use `cat` command,
   // here we need to ignore it.