RDBMS ANSI-SQL Compatible

SQL has different implementations and each of which may have extra features over the standard SQL or maybe not support some standard features.
You can see these links:

• https://www.altexsoft.com/blog/business/comparing-database-management-systems-mysql-postgresql-mssql-server-mongodb-elasticsearch-and-others/

• https://en.wikipedia.org/wiki/SQL#Standardization

• https://troels.arvin.dk/db/rdbms/