Which DBMSs have you worked with, which ones have you used more or less, and at what level?

In my practice, I have worked with several DBMS:

• PostgreSQL — most frequently used for developing and supporting business applications. Level — schema design, writing complex SQL queries, index optimization, working with transactions and triggers.

• MySQL — used for web projects, mainly at the query writing and replication setup level.

• MongoDB — used for projects with unstructured data, at the level of designing collections and writing aggregation queries.

• Oracle — had experience at the level of reading documentation and writing simple queries within the support of existing systems.

Thus, my main focus has been on relational DBMS, especially PostgreSQL, with a deep understanding of architecture and optimization.