fix: recognise set operation quantifiers written in any case

src/main/java/net/sf/jsqlparser/statement/select/SetOperation.java

@@ -20,19 +20,35 @@ public String getModifier() {
     }
 
     public boolean isAll() {
-        return modifier != null && modifier.contains("ALL");
+        return leadsWith("ALL");
     }
 
     public void setAll(boolean all) {
-        this.modifier = "ALL";
+        this.modifier = all ? "ALL" : "";
     }
 
     public boolean isDistinct() {
-        return modifier != null && modifier.contains("DISTINCT");
+        return leadsWith("DISTINCT");
     }
 
     public void setDistinct(boolean distinct) {
-        this.modifier = "DISTINCT";
+        this.modifier = distinct ? "DISTINCT" : "";
+    }
+
+    /**
+     * Whether the modifier opens with {@code keyword}, which the grammar records verbatim from the
+     * source and so may be written in any case. Anchored at the start and required to end on a word
+     * boundary, so a {@code CORRESPONDING BY NAME MATCHING(all)} column list cannot be mistaken for
+     * the ALL quantifier.
+     */
+    private boolean leadsWith(String keyword) {
+        if (modifier == null) {
+            return false;
+        }
+        String trimmed = modifier.trim();
+        return trimmed.regionMatches(true, 0, keyword, 0, keyword.length())
+                && (trimmed.length() == keyword.length()
+                        || !Character.isLetterOrDigit(trimmed.charAt(keyword.length())));
     }
 
     private final SetOperationType type;

src/test/java/net/sf/jsqlparser/statement/select/SetOperationModifierTest.java

@@ -16,6 +16,7 @@
 import net.sf.jsqlparser.JSQLParserException;
 import net.sf.jsqlparser.parser.CCJSqlParserUtil;
 import net.sf.jsqlparser.statement.Statement;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.parallel.Execution;
 import org.junit.jupiter.api.parallel.ExecutionMode;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -50,6 +51,72 @@ void testSetOperationModifierRoundTrip(String sql) throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed(sql);
     }
 
+    /**
+     * The grammar records the modifier verbatim from the source, so the quantifier survives in
+     * whatever case it was written. Every case spells the same set operation.
+     *
+     * @see <a href="https://github.com/JSQLParser/JSqlParser/issues/2419">#2419</a>
+     */
+    @ParameterizedTest
+    @ValueSource(strings = {"ALL", "all", "All", "aLL"})
+    void testAllModifierRecognisedInAnyCase(String quantifier) throws JSQLParserException {
+        SetOperation operation = firstOperation(
+                "SELECT a FROM t1 UNION " + quantifier + " SELECT a FROM t2");
+        assertTrue(operation.isAll(), "UNION " + quantifier + " should be an ALL union");
+        assertFalse(operation.isDistinct(), "UNION " + quantifier + " is not DISTINCT");
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"DISTINCT", "distinct", "Distinct"})
+    void testDistinctModifierRecognisedInAnyCase(String quantifier) throws JSQLParserException {
+        SetOperation operation = firstOperation(
+                "SELECT a FROM t1 UNION " + quantifier + " SELECT a FROM t2");
+        assertTrue(operation.isDistinct(), "UNION " + quantifier + " should be a DISTINCT union");
+        assertFalse(operation.isAll(), "UNION " + quantifier + " is not ALL");
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"EXCEPT", "INTERSECT", "MINUS"})
+    void testAllModifierRecognisedInAnyCaseForEverySetOperation(String setOperation)
+            throws JSQLParserException {
+        assertTrue(firstOperation("SELECT a FROM t1 " + setOperation + " all SELECT a FROM t2")
+                .isAll(), setOperation + " all should be an ALL operation");
+    }
+
+    /**
+     * A plain set operation carries no quantifier, and neither predicate may claim one.
+     */
+    @Test
+    void testUnqualifiedSetOperationIsNeitherAllNorDistinct() throws JSQLParserException {
+        SetOperation operation = firstOperation("SELECT a FROM t1 UNION SELECT a FROM t2");
+        assertFalse(operation.isAll());
+        assertFalse(operation.isDistinct());
+    }
+
+    /**
+     * The setters record what they are told rather than the keyword they are named after.
+     */
+    @Test
+    void testSettersHonourTheirArgument() {
+        UnionOp union = new UnionOp();
+
+        union.setAll(true);
+        assertTrue(union.isAll());
+        union.setAll(false);
+        assertFalse(union.isAll(), "setAll(false) must not leave an ALL modifier behind");
+
+        union.setDistinct(true);
+        assertTrue(union.isDistinct());
+        union.setDistinct(false);
+        assertFalse(union.isDistinct(), "setDistinct(false) must not leave a DISTINCT modifier");
+    }
+
+    private static SetOperation firstOperation(String sql) throws JSQLParserException {
+        Statement statement = CCJSqlParserUtil.parse(sql);
+        assertInstanceOf(SetOperationList.class, statement);
+        return ((SetOperationList) statement).getOperations().get(0);
+    }
+
     @ParameterizedTest
     @MethodSource("provideModifierLeakCases")
     void testModifierDoesNotLeakBetweenOperators(String sql, String forbidden)