3 levels of SQL expertise

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What is the extent of your knowledge of SQL? Basic, intermediate or advanced?

• Basic: simple select queries with filtering, inner and left joins, aggregation, confident use of date functions, CASE statement, UNIONs etc., then state that you can create SQL queries to a basic level.
• Intermediate: CTEs and temp tables, window functions, string handling functions (like REPLACE, SUBSTRING, LEFT, RIGHT, CHARINDEX), do numeric calculations, handle NULLs (with ISNULL, COALESCE and NULLIF), CAST and CONVERT data types, use derived tables and subqueries, then make it clear that you have intermediate SQL skills.
• If you can handle all the above plus strong data manipulation knowledge including PIVOT, recursion, use correlated subqueries, build ETL processes in code, create stored procs, functions and views, indexing, loops, dynamic SQL and have a good understanding of collation and optimisation, then let them know that you have advanced SQL knowledge and skills.

It’s important that you give an accurate assessment of your level.

Here are five SQL examples that demonstrate various basic SQL operations, including simple SELECT queries with filtering, INNER and LEFT JOINs, aggregation, confident use of date functions, CASE statements, and UNIONs.