fix: report ALTER TABLE actions that delete rows as MODIFIES_DATA (#2894)

StatementFeatureVisitor classified every ALTER TABLE as schema-only, so
TRUNCATE PARTITION, DROP PARTITION, EXCHANGE PARTITION and DISCARD or
IMPORT TABLESPACE passed a guard checking mayModifyData(), which is the
guard TRUNCATE and DROP carry MODIFIES_DATA for. They now report it as
certain, REPAIR PARTITION as possible like REPAIR TABLE, and an action
the grammar keeps as raw tokens (e.g. ClickHouse ALTER TABLE t DELETE
WHERE ..) as possible with the "unsupported" marker.

Author: tanjiroK-coder

src/main/java/net/sf/jsqlparser/statement/StatementFeatureVisitor.java

@@ -25,6 +25,8 @@
 import net.sf.jsqlparser.expression.TranscodingFunction;
 import net.sf.jsqlparser.parser.CCJSqlParserUtil;
 import net.sf.jsqlparser.statement.alter.Alter;
+import net.sf.jsqlparser.statement.alter.AlterExpression;
+import net.sf.jsqlparser.statement.alter.AlterOperation;
 import net.sf.jsqlparser.statement.alter.AlterCollation;
 import net.sf.jsqlparser.statement.alter.AlterRoutine;
 import net.sf.jsqlparser.statement.alter.AlterTrigger;
@@ -171,6 +173,16 @@
 @SuppressWarnings({"PMD.CyclomaticComplexity", "PMD.TooManyMethods", "PMD.ExcessiveImports"})
 public class StatementFeatureVisitor extends StatementVisitorAdapter<Void> {
 
+    /**
+     * ALTER TABLE actions that delete, swap or replace the rows of a table or partition. Like
+     * TRUNCATE and DROP they carry MODIFIES_DATA as well as MODIFIES_SCHEMA.
+     */
+    private static final Set<AlterOperation> ALTER_ACTIONS_MODIFYING_DATA =
+            EnumSet.of(AlterOperation.DROP_PARTITION, AlterOperation.TRUNCATE_PARTITION,
+                    AlterOperation.EXCHANGE_PARTITION, AlterOperation.DISCARD_PARTITION,
+                    AlterOperation.DISCARD_TABLESPACE, AlterOperation.IMPORT_PARTITION,
+                    AlterOperation.IMPORT_TABLESPACE);
+
     private final Analysis analysis;
 
     // ---- construction -----------------------------------------------------------------------
@@ -672,7 +684,25 @@ public <S> Void visit(PurgeStatement purgeStatement, S context) {
 
     @Override
     public <S> Void visit(Alter alter, S context) {
-        return schemaOnly();
+        schemaOnly();
+        if (alter.getAlterExpressions() == null) {
+            return null;
+        }
+        for (AlterExpression action : alter.getAlterExpressions()) {
+            AlterOperation operation = action.getOperation();
+            if (ALTER_ACTIONS_MODIFYING_DATA.contains(operation)) {
+                analysis.certain(StmtFeature.MODIFIES_DATA);
+            } else if (operation == AlterOperation.REPAIR_PARTITION) {
+                // like REPAIR TABLE, it may rewrite or discard rows
+                analysis.possible(StmtFeature.MODIFIES_DATA);
+            } else if (operation == AlterOperation.UNSPECIFIC) {
+                // an action the grammar does not model is kept as raw tokens and may write
+                // rows, e.g. ClickHouse's ALTER TABLE t DELETE WHERE ..
+                analysis.possible(StmtFeature.MODIFIES_DATA);
+                analysis.unresolved("unsupported");
+            }
+        }
+        return null;
     }
 
     @Override

src/site/sphinx/usage.rst

@@ -1209,7 +1209,7 @@ The features
       - ``SELECT``, ``DELETE .. RETURNING``, ``SHOW``, ``DESCRIBE``, ``EXPLAIN``
     * - ``MODIFIES_DATA``
       - rows are written or destroyed
-      - ``INSERT``, ``UPDATE``, ``DELETE``, ``MERGE``, ``UPSERT``, ``TRUNCATE``, ``DROP``
+      - ``INSERT``, ``UPDATE``, ``DELETE``, ``MERGE``, ``UPSERT``, ``TRUNCATE``, ``DROP``, ``ALTER TABLE .. TRUNCATE PARTITION``
     * - ``MODIFIES_SCHEMA``
       - the catalogue changes
       - ``CREATE``, ``ALTER``, ``DROP``, ``TRUNCATE``, ``GRANT``, ``COMMENT``

src/test/java/net/sf/jsqlparser/statement/StatementFeatureVisitorTest.java

@@ -255,6 +255,45 @@ void destructiveDdlAlsoModifiesData() throws JSQLParserException {
         }
     }
 
+    /**
+     * The ALTER TABLE actions that delete, swap or replace rows are destructive DDL in the same
+     * sense: {@code TRUNCATE PARTITION ALL} empties a partitioned table just like TRUNCATE.
+     */
+    @ParameterizedTest
+    @ValueSource(strings = {"ALTER TABLE t TRUNCATE PARTITION ALL",
+            "ALTER TABLE t TRUNCATE PARTITION p0", "ALTER TABLE t DROP PARTITION p0, p1",
+            "ALTER TABLE t ADD COLUMN c INT, DROP PARTITION p0",
+            "ALTER TABLE t EXCHANGE PARTITION p0 WITH TABLE u",
+            "ALTER TABLE t DISCARD TABLESPACE", "ALTER TABLE t DISCARD PARTITION p0 TABLESPACE",
+            "ALTER TABLE t IMPORT TABLESPACE", "ALTER TABLE t IMPORT PARTITION p0 TABLESPACE"})
+    void destructiveAlterActionsAlsoModifyData(String sql) throws JSQLParserException {
+        StatementFeatures f = analyse(sql);
+        assertThat(f.modifiesSchema()).isTrue();
+        assertThat(f.modifiesData()).isTrue();
+        assertThat(f.returnsResultSet()).isFalse();
+    }
+
+    /**
+     * An ALTER TABLE action the grammar does not model, such as ClickHouse's DELETE and UPDATE
+     * mutations, is kept as raw text, so a write cannot be excluded.
+     */
+    @ParameterizedTest
+    @ValueSource(strings = {"ALTER TABLE t DELETE WHERE id > 0",
+            "ALTER TABLE t UPDATE c = 1 WHERE id > 0"})
+    void unmodelledAlterActionMayModifyData(String sql) throws JSQLParserException {
+        StatementFeatures f = analyse(sql);
+        assertThat(f.modifiesSchema()).isTrue();
+        assertThat(f.mayModifyData()).isTrue();
+        assertThat(f.getUnresolvedReferences()).containsExactly("unsupported");
+    }
+
+    @Test
+    void repairPartitionMayModifyDataLikeRepairTable() throws JSQLParserException {
+        StatementFeatures f = analyse("ALTER TABLE t REPAIR PARTITION p0");
+        assertThat(f.modifiesData()).isFalse();
+        assertThat(f.mayModifyData()).isTrue();
+    }
+
     // ---- the cases a flag union gets wrong --------------------------------------------------
 
     @Test