fix: preserve JSON_TABLE EXISTS column order (#2682)

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

Author: minleejae

src/main/java/net/sf/jsqlparser/expression/JsonTableFunction.java

@@ -620,9 +620,6 @@ public String toString() {
                 builder.append(" FOR ORDINALITY");
                 return builder.toString();
             }
-            if (exists) {
-                builder.append(" EXISTS");
-            }
             if (dataType != null) {
                 builder.append(" ").append(dataType);
             }
@@ -637,6 +634,9 @@ public String toString() {
                 builder.append(scalarsType);
                 builder.append(" SCALARS");
             }
+            if (exists) {
+                builder.append(" EXISTS");
+            }
             if (wrapperClause != null && wrapperClause.isBeforePathExpression()) {
                 builder.append(" ").append(wrapperClause);
             }

src/test/java/net/sf/jsqlparser/expression/JsonTableExistsTest.java

@@ -0,0 +1,85 @@
+/*-
+ * #%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.expression;
+
+import net.sf.jsqlparser.JSQLParserException;
+import net.sf.jsqlparser.expression.JsonTableFunction.JsonTableValueColumnDefinition;
+import net.sf.jsqlparser.parser.AbstractJSqlParser.Dialect;
+import net.sf.jsqlparser.parser.CCJSqlParserUtil;
+import net.sf.jsqlparser.statement.create.table.ColDataType;
+import net.sf.jsqlparser.statement.select.PlainSelect;
+import net.sf.jsqlparser.statement.select.TableFunction;
+import net.sf.jsqlparser.test.TestUtils;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class JsonTableExistsTest {
+    @ParameterizedTest
+    @ValueSource(strings = {
+            "n INT EXISTS PATH '$.n'",
+            "n VARCHAR(10) EXISTS PATH '$.n'",
+            "NESTED PATH '$.items[*]' COLUMNS (n INT EXISTS PATH '$.n')"
+    })
+    void typedExistsRoundTrips(String column) throws JSQLParserException {
+        String sql = sql(column);
+        for (Dialect dialect : new Dialect[] {null, Dialect.MYSQL, Dialect.ORACLE}) {
+            PlainSelect select = (PlainSelect) TestUtils.assertSqlCanBeParsedAndDeparsed(sql,
+                    true, parser -> {
+                        if (dialect != null) {
+                            parser.withDialect(dialect);
+                        }
+                    });
+            TestUtils.assertSqlCanBeParsedAndDeparsed(select.toString(), false,
+                    parser -> {
+                        if (dialect != null) {
+                            parser.withDialect(dialect);
+                        }
+                    });
+        }
+    }
+
+    @Test
+    void typedExistsCanBeInspectedAndEdited() throws JSQLParserException {
+        PlainSelect select = (PlainSelect) CCJSqlParserUtil.parse(sql("n INT EXISTS PATH '$.n'"));
+        JsonTableFunction table =
+                (JsonTableFunction) ((TableFunction) select.getFromItem()).getFunction();
+        JsonTableValueColumnDefinition column =
+                (JsonTableValueColumnDefinition) table.getColumnsClause().getColumnDefinitions()
+                        .get(0);
+        assertTrue(column.isExists());
+        assertEquals("INT", column.getDataType().getBaseTypeName());
+        column.setColumnName("present").setDataType(new ColDataType("BIGINT"))
+                .setPathExpression(new StringValue("$.other"));
+        TestUtils.assertStatementCanBeDeparsedAs(select,
+                sql("present BIGINT EXISTS PATH '$.other'"), true);
+        TestUtils.assertSqlCanBeParsedAndDeparsed(select.toString());
+        column.setExistsKeyword(false);
+        TestUtils.assertStatementCanBeDeparsedAs(select, sql("present BIGINT PATH '$.other'"),
+                true);
+    }
+
+    @Test
+    void constructedAndUntypedExistsColumnsRetainOrder() throws JSQLParserException {
+        JsonTableValueColumnDefinition column = new JsonTableValueColumnDefinition()
+                .setColumnName("n").setExistsKeyword(true).setDataType(new ColDataType("INT"))
+                .setPathExpression(new StringValue("$.n"));
+        assertEquals("n INT EXISTS PATH '$.n'", column.toString());
+        column.setDataType(null);
+        assertEquals("n EXISTS PATH '$.n'", column.toString());
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sql(column.toString()));
+    }
+
+    private static String sql(String column) {
+        return "SELECT * FROM JSON_TABLE('[{\"n\":1},{}]', '$[*]' COLUMNS (" + column + ")) AS jt";
+    }
+}