diff --git a/crates/dbx-core/src/table_structure_sql.rs b/crates/dbx-core/src/table_structure_sql.rs
index 66b02783c..16ce82bfe 100644
--- a/crates/dbx-core/src/table_structure_sql.rs
+++ b/crates/dbx-core/src/table_structure_sql.rs
@@ -960,24 +960,26 @@ fn build_oracle_like_existing_column_sql(
         ));
         current_name = column.name.clone();
     }
-    if column.data_type.trim() != original.data_type.trim() {
-        statements.push(format!(
-            "ALTER TABLE {table} MODIFY ({} {});",
-            quote_ident(dialect, &current_name),
-            column_data_type(dialect, column)
-        ));
-    }
-    if column.is_nullable != original.is_nullable {
-        let nullability = if column.is_nullable { "NULL" } else { "NOT NULL" };
-        statements.push(format!("ALTER TABLE {table} MODIFY ({} {nullability});", quote_ident(dialect, &current_name)));
-    }
-    if normalize_default(Some(&column.default_value)) != original_default(column) {
+    let type_changed = column.data_type.trim() != original.data_type.trim();
+    let nullable_changed = column.is_nullable != original.is_nullable;
+    let default_changed = normalize_default(Some(&column.default_value)) != original_default(column);
+    if type_changed || nullable_changed || default_changed {
+        let data_type = column_data_type(dialect, column);
+        let mut parts = vec![quote_ident(dialect, &current_name), data_type];
+        // Always include nullability so the statement is self-contained (required by Dameng).
+        if !column.is_nullable {
+            parts.push("NOT NULL".to_string());
+        } else {
+            parts.push("NULL".to_string());
+        }
         let default_value = normalize_default(Some(&column.default_value));
-        let default_value = if default_value.is_empty() { "NULL".to_string() } else { default_value };
-        statements.push(format!(
-            "ALTER TABLE {table} MODIFY ({} DEFAULT {default_value});",
-            quote_ident(dialect, &current_name)
-        ));
+        if !default_value.is_empty() {
+            parts.push(format!("DEFAULT {default_value}"));
+        } else if default_changed {
+            // User cleared the default — explicitly drop it.
+            parts.push("DEFAULT NULL".to_string());
+        }
+        statements.push(format!("ALTER TABLE {table} MODIFY ({});", parts.join(" ")));
     }
     if clean(&column.comment) != original_comment(column) {
         let comment_value =
diff --git a/plugins/jdbc/src/main/java/app/dbx/jdbc/DbxJdbcPlugin.java b/plugins/jdbc/src/main/java/app/dbx/jdbc/DbxJdbcPlugin.java
index bf814f623..13f12ceee 100644
--- a/plugins/jdbc/src/main/java/app/dbx/jdbc/DbxJdbcPlugin.java
+++ b/plugins/jdbc/src/main/java/app/dbx/jdbc/DbxJdbcPlugin.java
@@ -1018,8 +1018,10 @@ public final class DbxJdbcPlugin {
         ArrayNode result = MAPPER.createArrayNode();
         String resolvedTable = oracleResolveTable(conn, owner, table);
         Set<String> pks = oraclePrimaryKeys(conn, owner, resolvedTable);
+        // data_default is a LONG column — it must be read first in JDBC, before any other
+        // column, otherwise the data is truncated. We put it at position 1 for this reason.
         String sql =
-            "SELECT c.column_name, c.data_type, c.nullable, c.data_default, " +
+            "SELECT c.data_default, c.column_name, c.data_type, c.nullable, " +
             "c.data_precision, c.data_scale, c.char_length, cc.comments " +
             "FROM all_tab_columns c " +
             "LEFT JOIN all_col_comments cc ON cc.owner = c.owner AND cc.table_name = c.table_name AND cc.column_name = c.column_name " +
@@ -1029,11 +1031,13 @@ public final class DbxJdbcPlugin {
             ps.setString(2, resolvedTable);
             try (ResultSet rs = ps.executeQuery()) {
                 while (rs.next()) {
+                    // data_default is a LONG — read it first, before all other columns.
+                    String dataDefault = rs.getString("data_default");
                     String name = rs.getString("column_name");
                     ObjectNode item = columnNode(result, name);
                     item.put("data_type", rs.getString("data_type"));
                     item.put("is_nullable", !"N".equals(rs.getString("nullable")));
-                    putNullablePreferValue(item, "column_default", rs.getString("data_default"));
+                    putNullablePreferValue(item, "column_default", dataDefault);
                     item.put("is_primary_key", pks.contains(name));
                     item.putNull("extra");
                     putNullablePreferValue(item, "comment", rs.getString("comments"));