Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires yiisoft/db-mssql dev-master -> satisfiable by yiisoft/db-mssql[dev-master]. - yiisoft/db-mssql dev-master requires yiisoft/db ^1.2 -> satisfiable by yiisoft/db[1.2.0] from composer repo (https://repo.packagist.org) but yiisoft/db is the root package and cannot be modified. See https://getcomposer.org/dep-on-root for details and assistance.