Use when writing or reviewing MSSQL/T-SQL, creating stored procedures, designing table schemas, writing views, building migrations, defining custom types, or architecting a SQL Server application database. Also use when writing RAISERROR patterns, CHECK constraints with scalar functions, base/subtype table hierarchies, composite key designs, role-scoped views with row-level security, or idempotent DDL scripts. If you are touching MSSQL for an application database, use this skill. Not for PostgreSQL, MySQL, Oracle, or SQLite — patterns are SQL Server-specific.