fix: allow DatabaseMetaData.getColumns to describe an unset scale (#1716

)

getColumns returns a 0 for the scale of a Decimal or Numeric column when the
scale is 0, and when the scale is null. The caller can then not differentiate
between a 0 or a null without another query.

This change replaces the 0 in the ResultSet for scale with a null when describing
an unscaled Decimal or Numeric column. getInt will still convert the null to a 0,
but the caller can then use wasNull() to find out if the underlying value was 0
or null.

This addresses Issue 1712. It is a breaking change, but if the correct getter
(getInt) is used for the column, there is no difference. Other getters may behave
differently.

Signed-off-by: crwr45 <charlie.wheelerrobinson@gmail.com>

pgjdbc/src/main/java/org/postgresql/jdbc/PgDatabaseMetaData.java

@@ -1636,7 +1636,12 @@ base type (-1 if base type does not use a typmod). -1 if this type is not a doma
         }
       }
       tuple[6] = connection.encodeString(Integer.toString(columnSize));
-      tuple[8] = connection.encodeString(Integer.toString(decimalDigits));
+      // Give null for an unset scale on Decimal and Numeric columns
+      if (((sqlType == Types.NUMERIC) || (sqlType == Types.DECIMAL)) && (typeMod == -1)) {
+        tuple[8] = null;
+      } else {
+        tuple[8] = connection.encodeString(Integer.toString(decimalDigits));
+      }
 
       // Everything is base 10 unless we override later.
       tuple[9] = connection.encodeString("10");

pgjdbc/src/test/java/org/postgresql/test/jdbc42/DatabaseMetaDataTest.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2007, PostgreSQL Global Development Group
+ * See the LICENSE file in the project root for more information.
+ */
+
+package org.postgresql.test.jdbc42;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.postgresql.test.TestUtil;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.sql.Connection;
+import java.sql.DatabaseMetaData;
+import java.sql.ResultSet;
+
+public class DatabaseMetaDataTest {
+
+  private Connection conn;
+
+  @Before
+  public void setUp() throws Exception {
+    conn = TestUtil.openDB();
+    TestUtil.createTable(conn, "decimaltest", "a decimal, b decimal(10, 5)");
+  }
+
+  @After
+  public void tearDown() throws Exception {
+    TestUtil.dropTable(conn, "decimaltest");
+    TestUtil.closeDB(conn);
+  }
+
+  @Test
+  public void testGetColumnsForNullScale() throws Exception {
+    DatabaseMetaData dbmd = conn.getMetaData();
+
+    ResultSet rs = dbmd.getColumns("%", "%", "decimaltest", "%");
+    assertTrue(rs.next());
+    assertEquals("a", rs.getString("COLUMN_NAME"));
+    assertEquals(0, rs.getInt("DECIMAL_DIGITS"));
+    assertTrue(rs.wasNull());
+
+    assertTrue(rs.next());
+    assertEquals("b", rs.getString("COLUMN_NAME"));
+    assertEquals(5, rs.getInt("DECIMAL_DIGITS"));
+    assertFalse(rs.wasNull());
+
+    assertTrue(!rs.next());
+  }
+}