feat: support MySQL named foreign key and check drops

Signed-off-by: minleejae <mmj9808@gmail.com>

Author: minleejae

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpression.java

@@ -504,6 +504,11 @@ public void setColumnOldName(String columnOldName) {
         this.columnOldName = columnOldName;
     }
 
+    /**
+     * Returns the constraint name, including any SQL identifier quotes. For named
+     * {@link AlterOperation#DROP_FOREIGN_KEY} and {@link AlterOperation#DROP_CHECK} actions, this
+     * is the deletion target; {@link #getPkColumns()} is not used.
+     */
     public String getConstraintName() {
         return this.constraintName;
     }
@@ -884,6 +889,7 @@ protected boolean isDropSpecialOperation() {
             case DROP_PRIMARY_KEY:
             case DROP_UNIQUE:
             case DROP_FOREIGN_KEY:
+            case DROP_CHECK:
                 return true;
             case DROP:
                 return columnName == null && pkColumns != null && !pkColumns.isEmpty();
@@ -1041,8 +1047,15 @@ protected void toStringDropSpecial(StringBuilder b) {
                 b.append("DROP UNIQUE (").append(PlainSelect.getStringList(pkColumns)).append(')');
                 break;
             case DROP_FOREIGN_KEY:
-                b.append("DROP FOREIGN KEY (").append(PlainSelect.getStringList(pkColumns))
-                        .append(')');
+                b.append("DROP FOREIGN KEY ");
+                if (constraintName != null) {
+                    b.append(constraintName);
+                } else {
+                    b.append('(').append(PlainSelect.getStringList(pkColumns)).append(')');
+                }
+                break;
+            case DROP_CHECK:
+                b.append("DROP CHECK ").append(constraintName);
                 break;
             default:
                 // Oracle Multi Column Drop

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpressionDrop.java

@@ -19,18 +19,11 @@ public class AlterExpressionDrop extends AlterExpression {
 
     @Override
     protected void appendBody(StringBuilder b) {
+        if (isDropSpecialOperation()) {
+            toStringDropSpecial(b);
+            return;
+        }
         switch (getOperation()) {
-            case DROP_PRIMARY_KEY:
-                b.append("DROP PRIMARY KEY ");
-                break;
-            case DROP_UNIQUE:
-                b.append("DROP UNIQUE (")
-                        .append(PlainSelect.getStringList(getPkColumns())).append(')');
-                break;
-            case DROP_FOREIGN_KEY:
-                b.append("DROP FOREIGN KEY (")
-                        .append(PlainSelect.getStringList(getPkColumns())).append(')');
-                break;
             case DROP_PARTITION:
                 b.append("DROP PARTITION ")
                         .append(PlainSelect.getStringList(getPartitions()));

src/main/java/net/sf/jsqlparser/statement/alter/AlterOperation.java

@@ -12,7 +12,7 @@
 import java.util.Locale;
 
 public enum AlterOperation {
-    ADD, ALTER, DROP, DROP_PRIMARY_KEY, DROP_UNIQUE, DROP_FOREIGN_KEY, MODIFY, CHANGE, CONVERT, COLLATE, ALGORITHM, RENAME, RENAME_TABLE, RENAME_INDEX, RENAME_KEY, RENAME_CONSTRAINT, COMMENT, COMMENT_WITH_EQUAL_SIGN, UNSPECIFIC, ADD_PARTITION, DROP_PARTITION, ATTACH_PARTITION, DETACH_PARTITION, DISCARD_PARTITION, IMPORT_PARTITION, TRUNCATE_PARTITION, COALESCE_PARTITION, REORGANIZE_PARTITION, EXCHANGE_PARTITION, ANALYZE_PARTITION, CHECK_PARTITION, OPTIMIZE_PARTITION, REBUILD_PARTITION, REPAIR_PARTITION, REMOVE_PARTITIONING, PARTITION_BY, SET_TABLE_OPTION, ENGINE, FORCE, KEY_BLOCK_SIZE, LOCK, DISCARD_TABLESPACE, IMPORT_TABLESPACE, DISABLE_KEYS, ENABLE_KEYS, ENABLE_ROW_LEVEL_SECURITY, DISABLE_ROW_LEVEL_SECURITY, FORCE_ROW_LEVEL_SECURITY, NO_FORCE_ROW_LEVEL_SECURITY, ALTER_PRIMARY_KEY;
+    ADD, ALTER, DROP, DROP_PRIMARY_KEY, DROP_UNIQUE, DROP_FOREIGN_KEY, DROP_CHECK, MODIFY, CHANGE, CONVERT, COLLATE, ALGORITHM, RENAME, RENAME_TABLE, RENAME_INDEX, RENAME_KEY, RENAME_CONSTRAINT, COMMENT, COMMENT_WITH_EQUAL_SIGN, UNSPECIFIC, ADD_PARTITION, DROP_PARTITION, ATTACH_PARTITION, DETACH_PARTITION, DISCARD_PARTITION, IMPORT_PARTITION, TRUNCATE_PARTITION, COALESCE_PARTITION, REORGANIZE_PARTITION, EXCHANGE_PARTITION, ANALYZE_PARTITION, CHECK_PARTITION, OPTIMIZE_PARTITION, REBUILD_PARTITION, REPAIR_PARTITION, REMOVE_PARTITIONING, PARTITION_BY, SET_TABLE_OPTION, ENGINE, FORCE, KEY_BLOCK_SIZE, LOCK, DISCARD_TABLESPACE, IMPORT_TABLESPACE, DISABLE_KEYS, ENABLE_KEYS, ENABLE_ROW_LEVEL_SECURITY, DISABLE_ROW_LEVEL_SECURITY, FORCE_ROW_LEVEL_SECURITY, NO_FORCE_ROW_LEVEL_SECURITY, ALTER_PRIMARY_KEY;
 
     public static AlterOperation from(String operation) {
         return Enum.valueOf(AlterOperation.class, operation.toUpperCase(Locale.ROOT));

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -17053,6 +17053,12 @@ AlterExpression AlterExpressionDrop():
 {
     <K_DROP> { alterExp.setOperation(AlterOperation.DROP); }
     (
+        LOOKAHEAD({ Dialect.MYSQL.name().equals(getAsString(Feature.dialect))
+                && (getToken(1).kind == K_CHECK
+                    || getToken(1).kind == K_FOREIGN && getToken(2).kind == K_KEY
+                        && getToken(3).kind != OPENING_BRACKET) })
+        MySqlDropNamedConstraint(alterExp)
+        |
         (
             <K_PARTITION> {
                 alterExp = new AlterExpressionPartition();
@@ -17118,6 +17124,15 @@ AlterExpression AlterExpressionDrop():
     { return alterExp; }
 }
 
+/** A MySQL deletion target is a constraint name, not a list of key columns. */
+void MySqlDropNamedConstraint(AlterExpression alterExp):
+{ String name; }
+{
+    ( <K_FOREIGN> <K_KEY> { alterExp.setOperation(AlterOperation.DROP_FOREIGN_KEY); }
+      | <K_CHECK> { alterExp.setOperation(AlterOperation.DROP_CHECK); } )
+    name=RelObjectName() { alterExp.setConstraintName(name); }
+}
+
 /**
  * Parses partition maintenance operations within AlterExpression.
  * Handles: TRUNCATE/ANALYZE/CHECK/OPTIMIZE/REBUILD/REPAIR PARTITION,

src/site/sphinx/usage.rst

@@ -252,6 +252,29 @@ explicit index owners, without reporting catalog-only object names as tables.
 The statement deparser delegates real tables to its configured select deparser.
 MySQL ALGORITHM/LOCK tokens retain their order and optional equals signs.
 
+MySQL named constraint drops
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+With ``Dialect.MYSQL``, ``DROP FOREIGN KEY name`` and ``DROP CHECK name``
+expose the target through ``AlterExpression.getConstraintName()``. Inspect
+``getOperation()`` for ``DROP_FOREIGN_KEY`` or ``DROP_CHECK``. Identifier
+quotes are preserved, and changing the name changes both SQL renderers.
+These named targets do not populate the legacy ``getPkColumns()`` list.
+
+.. code-block:: java
+
+    Alter alter = (Alter) CCJSqlParserUtil.parse(
+        "ALTER TABLE child DROP FOREIGN KEY fk_parent",
+        parser -> parser.withDialect(Dialect.MYSQL));
+    AlterExpression drop = alter.getAlterExpressions().get(0);
+    drop.setConstraintName("fk_customer");
+    // ALTER TABLE child DROP FOREIGN KEY fk_customer
+    String sql = alter.toString();
+
+    // The same API also supports constructing an action without parsing SQL.
+    AlterExpression checkDrop = new AlterExpression()
+        .withOperation(AlterOperation.DROP_CHECK).withConstraintName("positive_id");
+
 Inspect PostgreSQL schema statements
 ------------------------------------
 

src/test/java/net/sf/jsqlparser/statement/alter/MySqlDropConstraintTest.java

@@ -0,0 +1,91 @@
+/*-
+ * #%L
+ * JSQLParser library
+ * %%
+ * Copyright (C) 2004 - 2026 JSQLParser
+ * %%
+ * Dual licensed under GNU LGPL 2.1 or Apache License 2.0
+ * #L%
+ */
+package net.sf.jsqlparser.statement.alter;
+
+import static org.junit.jupiter.api.Assertions.*;
+import java.util.List;
+import net.sf.jsqlparser.JSQLParserException;
+import net.sf.jsqlparser.parser.AbstractJSqlParser.Dialect;
+import net.sf.jsqlparser.parser.CCJSqlParserUtil;
+import net.sf.jsqlparser.schema.Table;
+import net.sf.jsqlparser.util.deparser.StatementDeParser;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+class MySqlDropConstraintTest {
+    @ParameterizedTest
+    @ValueSource(strings = {"DROP FOREIGN KEY fk1", "DROP FOREIGN KEY `fk name`",
+            "DROP CHECK c1", "DROP CHECK `check name`",
+            "DROP FOREIGN KEY fk1, DROP CHECK c1",
+            "DROP FOREIGN KEY fk1, ALGORITHM = INPLACE, LOCK = NONE"})
+    void roundTripsNamedDrops(String actions) throws JSQLParserException {
+        Alter alter = parse("ALTER TABLE t " + actions);
+        assertEquals("ALTER TABLE t " + actions, alter.toString());
+        assertRoundTrip(alter);
+    }
+
+    @Test
+    void namesAndKindsAreEditableWithoutColumnLists() throws JSQLParserException {
+        Alter alter = parse("ALTER TABLE t DROP FOREIGN KEY fk1, DROP CHECK c1");
+        AlterExpression foreign = alter.getAlterExpressions().get(0);
+        AlterExpression check = alter.getAlterExpressions().get(1);
+        assertEquals(AlterOperation.DROP_FOREIGN_KEY, foreign.getOperation());
+        assertEquals("fk1", foreign.getConstraintName());
+        assertNull(foreign.getPkColumns());
+        assertEquals(AlterOperation.DROP_CHECK, check.getOperation());
+        assertEquals("c1", check.getConstraintName());
+        check.setConstraintName("`new check`");
+        foreign.setConstraintName("fk2");
+        assertEquals("ALTER TABLE t DROP FOREIGN KEY fk2, DROP CHECK `new check`",
+                alter.toString());
+        assertRoundTrip(alter);
+    }
+
+    @Test
+    void constructedActionsUseTheSameRendererAsParsedActions() throws JSQLParserException {
+        for (AlterOperation operation : List.of(AlterOperation.DROP_FOREIGN_KEY,
+                AlterOperation.DROP_CHECK)) {
+            Alter alter = new Alter();
+            alter.setTable(new Table("t"));
+            alter.addAlterExpression(new AlterExpression().withOperation(operation)
+                    .withConstraintName("`target constraint`"));
+            Alter parsed = parse(alter.toString());
+            assertEquals(operation, parsed.getAlterExpressions().get(0).getOperation());
+            assertEquals("`target constraint`",
+                    parsed.getAlterExpressions().get(0).getConstraintName());
+            assertRoundTrip(alter);
+            // Editing the operation on either concrete class must have the same effect.
+            parsed.getAlterExpressions().get(0).setOperation(AlterOperation.DROP_CHECK);
+            assertEquals("ALTER TABLE t DROP CHECK `target constraint`", parsed.toString());
+        }
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"DROP FOREIGN KEY (id)", "DROP UNIQUE (a, b)",
+            "DROP PRIMARY KEY", "DROP CONSTRAINT IF EXISTS ck CASCADE", "DROP (a, b)",
+            "DROP COLUMN c", "DROP INDEX idx"})
+    void preservesDefaultDropForms(String action) throws JSQLParserException {
+        String sql = "ALTER TABLE t " + action;
+        Alter alter = (Alter) CCJSqlParserUtil.parse(sql);
+        assertEquals(sql, alter.toString().trim());
+    }
+
+    private static Alter parse(String sql) throws JSQLParserException {
+        return (Alter) CCJSqlParserUtil.parse(sql, p -> p.withDialect(Dialect.MYSQL));
+    }
+
+    private static void assertRoundTrip(Alter alter) throws JSQLParserException {
+        StringBuilder sql = new StringBuilder();
+        alter.accept(new StatementDeParser(sql), null);
+        assertEquals(alter.toString(), sql.toString());
+        assertEquals(alter.toString(), parse(sql.toString()).toString());
+    }
+}