There's no need to install the SSDT standalone installer for the core SSDT experience. Starting with Visual Studio 2017, the functionality of creating Database Projects has been integrated into the Visual Studio installation. SSDT for Visual Studio 2017 Changes in SSDT for Visual Studio 2017

Only one shell is installed per version of Visual Studio installing a second SSDT just adds the missing templates. Otherwise, you probably need to install multiple previous versions to get all of the templates used in SQL Server. To get all of the project templates together in one SSDT, you need the newest version. Previous versions came with distinct sets of project templates. Historically, the Visual Studio shell used to create SQL Server content types has been released under various names, including SQL Server Data Tools, SQL Server Data Tools - Business Intelligence, and Business Intelligence Development Studio. SSDT is backwards compatible, so you can always use the newest SSDT to design and deploy databases, models, reports, and packages that run on older versions of SQL Server. SQL Server Data Tools (SSDT) provides project templates and design surfaces for building SQL Server content types - relational databases, Analysis Services models, Reporting Services reports, and Integration Services packages. Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW)

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