Contoso Table Storage is the correct answer.

This choice describes a simple table storage model used by key value or basic NoSQL table services that do not enforce relationships between rows and that do not provide multi entity transactional guarantees. Because data is organized around partition and row keys there is no built in referential integrity and transactions that span multiple entities are not guaranteed. Filtering or sorting on attributes that are not part of the primary key is difficult and queries on non key fields can force full table scans or require external indexing to be efficient.

Cloud Bigtable is a high scale wide column NoSQL database designed for very large throughput and low latency. It supports row level atomicity and is optimized for range scans and time series patterns, so the simple table storage limitations described in the question are not the typical characterization of this managed service.

Cloud SQL for PostgreSQL is a relational database that provides ACID transactions, foreign keys, and rich indexing options. It therefore enforces referential integrity and supports complex queries without the table storage constraints in the question.

Cloud Spanner is a distributed relational database that offers strong consistency and global transactions along with SQL querying and schema constraints. It is explicitly designed to avoid the lack of transactional guarantees and integrity problems mentioned in the question.

Cloud SQL for MySQL is a managed MySQL service that supports transactions, foreign keys, and indexes, and it does not suffer from the lack of referential integrity and difficulty querying non key fields that the question describes.

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