SQL- Structured query language is a programming language that is used across the board for different database tools such as Microsoft access, Microsoft SQL Server, PostGreSQL and Oracle databases among others.
PowerBI and Tableau on the other hand are business intelligence tools.
It is important to understand that any BA involved in an IT project, would at some point have to deal with database systems to dig out data required for their analysis. SQL would come in handy to the BA to get the data out of their system by writing their own queries.
As per the requirement of the data in the project, it can come up frequently in the requirement analysis phase for a BA. However, in my opinion the data is required throughout the project. This holds good for any methodology including iterative or agile. For example, data can be required in testing phase to test all the implemented functionalities of the system.
As addressed before, SQL is useful to query the database to get the required data. This is applicable for most of the projects.
However, the PowerBI and Tableau tools may be used in projects exclusively involving business intelligence and datawarehousing systems. Tableau is a visualization tool that helps the user in ad-hoc analysis of large sets of data. The BA can load data from multiple sources and join them together to create their own data and start analyzing it to find better insights.
PowerBI is also a visualization tool but it is better in terms of predictive modelling and reporting. It is a decent tool to build dashboards and reports for the management team. This is again useful in requirement gathering and analysis phase of the project.
However, depending on the project requirement these tools could be used in different phases of the project like coding, testing and implementation phases as well. For example, if the project is a business intelligence project that requires building dashboards for the executive team using business intelligence tools, the BA has to ensure the UAT is passed using the tools (Tableau, powerBI) for the project.
