Fix: ALTER INDEX COMMENT

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

@@ -538,6 +538,11 @@ public String toString() {
             b.append(' ').append(PlainSelect.getStringList(parameters, false, false));
         }
 
+        if (index != null && index.getCommentText() != null) {
+            // `USING` is a parameters
+            b.append(" COMMENT ").append(index.getCommentText());
+        }
+
         return b.toString();
     }
 

src/main/java/net/sf/jsqlparser/statement/create/table/Index.java

@@ -143,11 +143,6 @@ public String toString() {
             return head;
         }
 
-        // MYSQL: ALTER TABLE ADD INDEX COMMENT 'comment'
-        if (getCommentText() != null) {
-            return head + " " + tail + " COMMENT " + getCommentText();
-        }
-
         return head + " " + tail;
     }
 

src/main/java/net/sf/jsqlparser/statement/create/table/NamedConstraint.java

@@ -21,12 +21,6 @@ public String toString() {
         String head = getName() != null ? "CONSTRAINT " + getName() + " " : "";
         String tail = getType() + " " + PlainSelect.getStringList(getColumnsNames(), true, true) +
                 (!"".equals(idxSpecText) ? " " + idxSpecText : "");
-
-        // MYSQL: ALTER TABLE ADD CONSTRAINT COMMENT 'comment'
-        if (getCommentText() != null) {
-            return head + tail + " COMMENT " + getCommentText();
-        }
-
         return head + tail;
     }
 

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

@@ -6256,9 +6256,9 @@ AlterExpression AlterExpression():
                     index = new Index().withType(tk.image).withName(sk3).withColumnsNames(columnNames);
                     alterExp.setIndex(index);
                   }
-                  [ index = IndexWithComment(index) { alterExp.setIndex(index); } ]
                   constraints=AlterExpressionConstraintState() { alterExp.setConstraints(constraints); }
                   [<K_USING> sk4=RelObjectName() { alterExp.addParameters("USING", sk4); }]
+                  [ index = IndexWithComment(index) { alterExp.setIndex(index); } ]
                 )
                 |
                 LOOKAHEAD(3) (

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

@@ -1,3 +1,12 @@
+/*-
+ * #%L
+ * JSQLParser library
+ * %%
+ * Copyright (C) 2004 - 2023 JSQLParser
+ * %%
+ * Dual licensed under GNU LGPL 2.1 or Apache License 2.0
+ * #L%
+ */
 package net.sf.jsqlparser.expression;
 
 import net.sf.jsqlparser.JSQLParserException;

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

@@ -483,6 +483,23 @@ public void testIssue679() throws JSQLParserException {
                 "ALTER TABLE tb_session_status ADD INDEX idx_user_id_name (user_id, user_name(10)), ADD INDEX idx_user_name (user_name)");
     }
 
+    @Test
+    public void testAlterTableColumnCommentIssue1926() throws JSQLParserException {
+        String statement =
+                "ALTER TABLE `student` ADD INDEX `idx_age` (`age`) USING BTREE COMMENT 'index age'";
+        assertSqlCanBeParsedAndDeparsed(statement);
+
+        String stmt2 =
+                "ALTER TABLE `student` ADD INDEX `idx_name` (`name`) COMMENT 'index name', " +
+                        "ADD INDEX `idx_age` (`age`) USING BTREE COMMENT 'index age'";
+        assertSqlCanBeParsedAndDeparsed(stmt2);
+
+        // TODO NOT SUPPORT MYSQL: ADD {INDEX | KEY} `idx_age` USING BTREE (`age`)
+        // String stmt3 = "ALTER TABLE `student` ADD INDEX `idx_age` USING BTREE (`age`) COMMENT
+        // 'index age'";
+        // assertSqlCanBeParsedAndDeparsed(stmt3);
+    }
+
     @Test
     public void testAlterTableIndex586() throws Exception {
         Statement result =