IGNITE-29129 SQL Calcite: Fix CAST to VARCHAR for unmapped Java types

modules/calcite/src/main/java/org/apache/ignite/internal/processors/query/calcite/type/IgniteTypeFactory.java

@@ -296,7 +296,11 @@ else if (type instanceof IgniteCustomType)
                 return customType;
         }
 
-        return toSql(this, type);
+        RelDataType sqlType = toSql(this, type);
+
+        // Java types without a built-in SQL mapping must use Ignite's OTHER semantics, including casts.
+        return sqlType.getSqlTypeName() == SqlTypeName.OTHER
+            ? createCustomType(Object.class, sqlType.isNullable()) : sqlType;
     }
 
     /** Converts Java types, including Java time types, to SQL types using the supplied factory. */

modules/calcite/src/test/java/org/apache/ignite/internal/processors/query/calcite/integration/DataTypesTest.java

@@ -1125,6 +1125,23 @@ public void testCharToVarcharConversion() {
             .check();
     }
 
+    /** */
+    @Test
+    public void testOtherTypeCastToVarchar() {
+        sql("CREATE TABLE t(id INT PRIMARY KEY, oth OTHER) WITH " + atomicity());
+
+        sql("INSERT INTO t VALUES (1, 'str'), (2, 42), (3, NULL)");
+
+        assertQuery("SELECT CAST(id AS VARCHAR), CAST(oth AS VARCHAR) FROM t ORDER BY id")
+            .ordered()
+            .returns("1", "str")
+            .returns("2", "42")
+            .returns("3", null)
+            .check();
+
+        assertQuery("SELECT id FROM t WHERE CAST(oth AS VARCHAR) = '42'").returns(2).check();
+    }
+
     /** */
     private void assumeNoTransactions() {
         assumeTrue(sqlTxMode == SqlTransactionMode.NONE, "Test use queries that doesn't touch any data. Skip for tx modes");

modules/calcite/src/test/java/org/apache/ignite/internal/processors/query/calcite/integration/SystemViewsIntegrationTest.java

@@ -17,6 +17,7 @@
 
 package org.apache.ignite.internal.processors.query.calcite.integration;
 
+import java.math.BigDecimal;
 import java.sql.Date;
 import java.util.Collection;
 import org.apache.ignite.cluster.ClusterNode;
@@ -59,6 +60,46 @@ public void testMetricsView() {
         assertQuery("SELECT value FROM sys.metrics WHERE name = 'cluster.TotalClientNodes'").returns("1").check();
     }
 
+    /** */
+    @Test
+    public void testClassColumn() {
+        sql("CREATE TABLE t(id INT PRIMARY KEY, name VARCHAR, amount DECIMAL(10, 2))");
+
+        assertQuery("SELECT CAST(\"TYPE\" AS VARCHAR) AS TYPE_NAME FROM SYS.TABLE_COLUMNS;")
+            .returns(Object.class.toString())
+            .returns(Integer.class.toString())
+            .returns(Integer.class.toString())
+            .returns(String.class.toString())
+            .returns(BigDecimal.class.toString())
+            .check();
+
+        assertQuery("SELECT COLUMN_NAME, \"TYPE\" FROM SYS.TABLE_COLUMNS")
+            .returns("_VAL", Object.class)
+            .returns("_KEY", Integer.class)
+            .returns("ID", Integer.class)
+            .returns("NAME", String.class)
+            .returns("AMOUNT", BigDecimal.class)
+            .check();
+
+        assertQuery("SELECT COLUMN_NAME FROM SYS.TABLE_COLUMNS WHERE CAST(\"TYPE\" AS VARCHAR) = ?")
+            .withParams(String.class.toString())
+            .returns("NAME")
+            .check();
+
+        // Creating Ignite's OTHER type must not affect Class-valued system view columns.
+        sql("CREATE TABLE other_seed(id INT PRIMARY KEY, val OTHER)");
+        sql("INSERT INTO other_seed VALUES (1, 'seed')");
+        assertQuery("SELECT val FROM other_seed").returns("seed").check();
+
+        assertQuery("SELECT CAST(\"TYPE\" AS VARCHAR) AS TYPE_NAME FROM SYS.TABLE_COLUMNS WHERE TABLE_NAME = 'T'")
+            .returns(Object.class.toString())
+            .returns(Integer.class.toString())
+            .returns(Integer.class.toString())
+            .returns(String.class.toString())
+            .returns(BigDecimal.class.toString())
+            .check();
+    }
+
     /** */
     @Test
     public void testFiltrableView() {

modules/calcite/src/test/java/org/apache/ignite/internal/processors/query/calcite/type/OtherTypeTest.java

@@ -65,4 +65,20 @@ public void testTypeInterning() {
                 calciteFactory.createSqlType(SqlTypeName.OTHER), nullable));
         }
     }
+
+    /** */
+    @Test
+    public void testJavaTypeConversion() {
+        IgniteTypeFactory factory = new IgniteTypeFactory();
+
+        for (boolean nullable : new boolean[] {false, true}) {
+            RelDataType javaType = factory.createTypeWithNullability(factory.createJavaType(Class.class), nullable);
+            RelDataType sqlType = factory.toSql(javaType);
+
+            assertEquals(OtherType.class, sqlType.getClass());
+            assertEquals(SqlTypeName.ANY, sqlType.getSqlTypeName());
+            assertEquals(nullable, sqlType.isNullable());
+            assertSame(factory.createCustomType(Object.class, nullable), sqlType);
+        }
+    }
 }