mysql5 if not exists emulation

mysql5.if_not_exists.sql

--- if not exists index
SET @dbname = DATABASE();
SET @tablename = "TABLENAME";
SET @indexname = "INDEXNAME";
SET @preparedStatement =
   (SELECT IF (EXISTS
                 (SELECT COUNT(*)
                  FROM information_schema.statistics
                  WHERE (table_schema = @dbname)
                    AND (table_name = @tablename)
                    AND (index_name = @indexname) ) > 0,
                      "SELECT 1",
                      CONCAT("ALTER TABLE ", @tablename, " ADD CONSTRAINT ", @indexname, " UNIQUE KEY(<keys...>);")));
 
 PREPARE alterIfNotExists
 FROM @preparedStatment;
 EXECUTE alterIfNotExists;
 DEALLOCATE PREPARE alterIfNotExists;
 --- if not exists column
SET @dbname = DATABASE();
SET @tablename = "TABLENAME";
SET @columnname = "COLUMNNAME";
SET @preparedStatement =
  (SELECT IF(
               (SELECT COUNT(*)
                FROM INFORMATION_SCHEMA.COLUMNS
                WHERE (table_name = @tablename)
                  AND (table_schema = @dbname)
                  AND (column_name = @columnname) ) > 0, "SELECT 1", CONCAT("ALTER TABLE ", @tablename, " ADD ", @columnname, " text NOT NULL;")));
PREPARE alterIfNotExists
FROM @preparedStatement;
EXECUTE alterIfNotExists;
DEALLOCATE PREPARE alterIfNotExists;