SET @avatar_column_exists := (
    SELECT COUNT(*)
    FROM information_schema.COLUMNS
    WHERE TABLE_SCHEMA = DATABASE()
      AND TABLE_NAME = 'sys_user'
      AND COLUMN_NAME = 'avatar'
);

SET @avatar_column_sql := IF(
    @avatar_column_exists = 0,
    'ALTER TABLE `sys_user` ADD COLUMN `avatar` VARCHAR(255) NULL COMMENT ''头像'' AFTER `phone`',
    'SELECT ''sys_user.avatar already exists'''
);

PREPARE avatar_column_stmt FROM @avatar_column_sql;
EXECUTE avatar_column_stmt;
DEALLOCATE PREPARE avatar_column_stmt;