There are a lot of relational database tools like MySQL, MS SQL Server, Oracle, etc. You can learn any one of these tools. There is no such best SQL for data science. All these tools are almost similar with little differences.
The only thing a data scientist aspirant should focus is on understanding types of normalization, writing queries like nested queries, co-related queries, group by, having, and joining queries. Learning SQL can be helpful in the Hive of BigData analytics since Hive and SQL has a similar query language.
You can watch this video on SQL for data science for a better understanding: