Are there databases that don't have SQL? Well, for example, which work according to some other scheme and with other languages? What are these bases, if they exist?
There are, of course.
Key-valueDBMS (and they are also databases) with their own protocols.
- embeddable libraries offering direct API only. I only recall
sqlite– but it's SQL, and
berkeley db– and this
key-value. Well, I found
InfinityDBas an example for Java
- a lot of trendy
NoSQLgenerally don't use SQL. For example, the referenced
JSONbased query language.
Dataloglanguage, for example, which completely influenced the addition of recursive queries to SQL
- some sbd can support both SQL and some other protocol. For example, you can interact with
MySQLwithout using SQL – via
HandlerSocket. Moreover, SQL can be both the main language for a DBMS, and an alternative, sometimes offering fewer features, but added for compatibility.
Relational databases are pretty much all SQL now. But obviously there are student and academic experiments that SQL did not do. Some of them may even be developing, but something known was not found. For non-relational databases, the spread is much wider.
A separate interesting question is what exactly should be considered as SQL. A DBMS can provide a query language that only at first glance looks like SQL, without supporting a large number of features and behavior of the SQL standard, but with some of its own solutions.