#570: MySQL compatibility for ALTER TABLE .. DROP INDEX

h2/src/docsrc/html/changelog.html

@@ -21,6 +21,8 @@ Change Log
 
 <h2>Next Version (unreleased)</h2>
 <ul>
+<li>Issue #570: MySQL compatibility for ALTER TABLE .. DROP INDEX
+</li>
 <li>Issue #537: Include the COLUMN name in message "Numeric value out of range"
 </li>
 <li>Issue #600: ROW_NUMBER() behaviour change in H2 1.4.195

h2/src/main/org/h2/command/Parser.java

@@ -64,6 +64,7 @@ import org.h2.command.ddl.DropUserDataType;
 import org.h2.command.ddl.DropView;
 import org.h2.command.ddl.GrantRevoke;
 import org.h2.command.ddl.PrepareProcedure;
+import org.h2.command.ddl.SchemaCommand;
 import org.h2.command.ddl.SetComment;
 import org.h2.command.ddl.TruncateTable;
 import org.h2.command.dml.AlterSequence;
@@ -5791,9 +5792,18 @@ public class Parser {
                 return commandIfTableExists(schema, tableName, ifTableExists, command);
             } else if (readIf("INDEX")) {
                 // MySQL compatibility
-                String indexName = readIdentifierWithSchema();
-                DropIndex command = new DropIndex(session, getSchema());
-                command.setIndexName(indexName);
+                String indexOrConstraintName = readIdentifierWithSchema();
+                final SchemaCommand command;
+                if (schema.findIndex(session, indexOrConstraintName) != null) {
+                    DropIndex dropIndexCommand = new DropIndex(session, getSchema());
+                    dropIndexCommand.setIndexName(indexOrConstraintName);
+                    command = dropIndexCommand;
+                } else {
+                    AlterTableDropConstraint dropCommand = new AlterTableDropConstraint(
+                            session, getSchema(), false/*ifExists*/);
+                    dropCommand.setConstraintName(indexOrConstraintName);
+                    command = dropCommand;
+                }
                 return commandIfTableExists(schema, tableName, ifTableExists, command);
             } else if (readIf("PRIMARY")) {
                 read("KEY");

h2/src/test/org/h2/test/db/TestCompatibility.java

@@ -395,6 +395,10 @@ public class TestCompatibility extends TestBase {
 
         stat.execute("CREATE TABLE TEST2(ID INT) ROW_FORMAT=DYNAMIC");
 
+        // check the MySQL index dropping syntax
+        stat.execute("ALTER TABLE TEST_COMMENT_ENGINE ADD CONSTRAINT CommentUnique UNIQUE (SOME_ITEM_ID)");
+        stat.execute("ALTER TABLE TEST_COMMENT_ENGINE DROP INDEX CommentUnique");
+
         conn.close();
         conn = getConnection("compatibility");
     }