fix: accept identity RESTART values without WITH

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

@@ -61,6 +61,7 @@ public void setParameters(List<Sequence.Parameter> parameters) {
         this.parameters = parameters == null ? null : new ArrayList<>(parameters);
     }
 
+    /** Returns the restart value, or null for a bare RESTART using the sequence start value. */
     public Long getRestartWith() {
         return restartWith;
     }
@@ -69,6 +70,11 @@ public void setRestartWith(Long restartWith) {
         this.restartWith = restartWith;
     }
 
+    public IdentityAlteration withRestartWith(Long restartWith) {
+        setRestartWith(restartWith);
+        return this;
+    }
+
     public boolean isIfExists() {
         return ifExists;
     }

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

@@ -16306,7 +16306,7 @@ IdentityAlteration ColumnIdentityAlteration():
             }
         )
         |
-        <K_RESTART> [ LOOKAHEAD(2) <K_WITH> restart=SequenceParameterValue() ] {
+        <K_RESTART> [ LOOKAHEAD(1) [ <K_WITH> ] restart=SequenceParameterValue() ] {
             alteration = new IdentityAlteration(IdentityAlteration.Kind.RESTART);
             alteration.setRestartWith(restart);
         }

src/site/sphinx/usage.rst

@@ -293,6 +293,13 @@ Table constraints expose ``Index.getNullsDistinct()``, ``getIncludeColumns()``,
 
 Identity alterations are available as ``ColumnDataType.getIdentityAlterations()``. Sequence ownership is shared by ``CreateSequence`` and ``AlterSequence`` through ``Sequence.getOwnership()``: ``null`` means omitted, ``isNone()`` means explicit ``OWNED BY NONE``, and ``getColumn()`` identifies an owner. ``TablesNamesFinder`` includes ``LIKE`` sources and sequence owners without treating sequence or type names as tables. See `ALTER TABLE <https://www.postgresql.org/docs/18/sql-altertable.html>`_ and `ALTER SEQUENCE <https://www.postgresql.org/docs/18/sql-altersequence.html>`_.
 
+For identity columns, ``RESTART 20`` and ``RESTART WITH 20`` produce the same
+``IdentityAlteration`` with kind ``RESTART`` and ``getRestartWith() == 20L``.
+The renderer consistently uses ``RESTART WITH 20``. A null restart value means
+bare ``RESTART``, which uses the sequence's configured start value. Call
+``setRestartWith`` to edit a parsed action or construct one with
+``new IdentityAlteration(Kind.RESTART).withRestartWith(20L)``.
+
 
 Structured column attributes
 ============================

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

@@ -0,0 +1,84 @@
+/*-
+ * #%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.util.deparser.StatementDeParser;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+class IdentityRestartValueTest {
+    @ParameterizedTest
+    @ValueSource(strings = {"20", "WITH 20", "+20", "-20", "WITH -20", "9223372036854775807"})
+    void representsOptionalWithUsingTheSameValue(String value) throws JSQLParserException {
+        for (Dialect dialect : new Dialect[] {null, Dialect.POSTGRESQL}) {
+            Alter alter = parse("ALTER TABLE t ALTER COLUMN id RESTART " + value, dialect);
+            IdentityAlteration restart = identity(alter).get(0);
+            assertEquals(IdentityAlteration.Kind.RESTART, restart.getKind());
+            assertEquals(Long.valueOf(value.replace("WITH ", "")), restart.getRestartWith());
+            roundTrip(alter, dialect);
+        }
+    }
+
+    @Test
+    void editsAndConstructsRestartAndPreservesBareRestart() throws JSQLParserException {
+        Alter alter = parse("ALTER TABLE t ALTER COLUMN id RESTART", Dialect.POSTGRESQL);
+        assertNull(identity(alter).get(0).getRestartWith());
+        identity(alter).get(0).setRestartWith(20L);
+        assertEquals("ALTER TABLE t ALTER COLUMN id RESTART WITH 20", alter.toString());
+        roundTrip(alter, Dialect.POSTGRESQL);
+        alter.getAlterExpressions().get(0).getColDataTypeList().get(0).setIdentityAlterations(
+                List.of(new IdentityAlteration(IdentityAlteration.Kind.RESTART)
+                        .withRestartWith(40L)));
+        assertEquals("ALTER TABLE t ALTER COLUMN id RESTART WITH 40", alter.toString());
+        roundTrip(alter, Dialect.POSTGRESQL);
+        identity(alter).get(0).setRestartWith(null);
+        assertEquals("ALTER TABLE t ALTER COLUMN id RESTART", alter.toString());
+    }
+
+    @Test
+    void respectsIdentityAndAlterActionBoundaries() throws JSQLParserException {
+        Alter alter = parse(
+                "ALTER TABLE t ALTER COLUMN id SET CACHE 10 RESTART 20 SET NO CYCLE, ADD COLUMN extra INT",
+                Dialect.POSTGRESQL);
+        assertEquals(3, identity(alter).size());
+        assertEquals(2, alter.getAlterExpressions().size());
+        roundTrip(alter, Dialect.POSTGRESQL);
+        roundTrip(parse("ALTER TABLE t ALTER COLUMN id RESTART SET CACHE 10", Dialect.POSTGRESQL),
+                Dialect.POSTGRESQL);
+        assertThrows(JSQLParserException.class,
+                () -> parse("ALTER TABLE t ALTER COLUMN id RESTART WITH", Dialect.POSTGRESQL));
+    }
+
+    private static List<IdentityAlteration> identity(Alter alter) {
+        return alter.getAlterExpressions().get(0).getColDataTypeList().get(0)
+                .getIdentityAlterations();
+    }
+
+    private static Alter parse(String sql, Dialect dialect) throws JSQLParserException {
+        return (Alter) CCJSqlParserUtil.parse(sql, p -> {
+            if (dialect != null) {
+                p.withDialect(dialect);
+            }
+        });
+    }
+
+    private static void roundTrip(Alter alter, Dialect dialect) throws JSQLParserException {
+        StringBuilder sql = new StringBuilder();
+        alter.accept(new StatementDeParser(sql), null);
+        assertEquals(alter.toString(), sql.toString());
+        assertEquals(sql.toString(), parse(sql.toString(), dialect).toString());
+    }
+}