If youโre a Data Analyst, chances are you use ๐๐๐ every single day. And if youโre preparing for interviews, youโve probably realized that it's not just about writing queries it's about writing smart, efficient, and scalable ones.
- ๐๐ซ๐๐๐ค ๐๐ญ ๐๐จ๐ฐ๐ง ๐ฐ๐ข๐ญ๐ก ๐๐๐๐ฌ (๐๐จ๐ฆ๐ฆ๐จ๐ง ๐๐๐๐ฅ๐ ๐๐ฑ๐ฉ๐ซ๐๐ฌ๐ฌ๐ข๐จ๐ง๐ฌ)
Ever worked on a query that became an unreadable monster? CTEs let you break that down into logical steps. You can treat them like temporary views โ great for simplifying logic and improving collaboration across your team.
- ๐๐ฌ๐ ๐๐ข๐ง๐๐จ๐ฐ ๐ ๐ฎ๐ง๐๐ญ๐ข๐จ๐ง๐ฌ
Forget the mess of subqueries. With functions like ROW_NUMBER(), RANK(), LEAD() and LAG(), you can compare rows, rank items, or calculate running totals โ all within the same query. Total
- ๐๐ฎ๐๐ช๐ฎ๐๐ซ๐ข๐๐ฌ (๐๐๐ฌ๐ญ๐๐ ๐๐ฎ๐๐ซ๐ข๐๐ฌ)
Yes, they're old school, but nested subqueries are still powerful. Use them when you want to filter based on results of another query or isolate logic step-by-step before joining with the big picture.
- ๐๐ง๐๐๐ฑ๐๐ฌ & ๐๐ฎ๐๐ซ๐ฒ ๐๐ฉ๐ญ๐ข๐ฆ๐ข๐ณ๐๐ญ๐ข๐จ๐ง
Query taking forever? Look at your indexes. Index the columns you use in JOINs, WHERE, and GROUP BY. Even basic knowledge of how the SQL engine reads data can take your skills up a notch.
- ๐๐จ๐ข๐ง๐ฌ ๐ฏ๐ฌ. ๐๐ฎ๐๐ช๐ฎ๐๐ซ๐ข๐๐ฌ
Joins are usually faster and better for combining large datasets. Subqueries, on the other hand, are cleaner when doing one-off filters or smaller operations. Choose wisely based on the context.
- ๐๐๐๐ ๐๐ญ๐๐ญ๐๐ฆ๐๐ง๐ญ๐ฌ:
Want to categorize or bucket data without creating a separate table? Use CASE. Itโs ideal for conditional logic, custom labels, and grouping in a single query.
- ๐๐ ๐ ๐ซ๐๐ ๐๐ญ๐ข๐จ๐ง๐ฌ & ๐๐๐๐๐ ๐๐
Most analytics questions start with "how many", "whatโs the average", or "which is the highest?". SUM(), COUNT(), AVG(), etc., and pair them with GROUP BY to drive insights that matter.
- ๐๐๐ญ๐๐ฌ ๐๐ซ๐ ๐๐ฅ๐ฐ๐๐ฒ๐ฌ ๐๐ซ๐ข๐๐ค๐ฒ
Time-based analysis is everywhere: trends, cohorts, seasonality, etc. Get familiar with functions like DATEADD, DATEDIFF, DATE_TRUNC, and DATEPART to work confidently with time series data.
- ๐๐๐ฅ๐-๐๐จ๐ข๐ง๐ฌ & ๐๐๐๐ฎ๐ซ๐ฌ๐ข๐ฏ๐ ๐๐ฎ๐๐ซ๐ข๐๐ฌ ๐๐จ๐ซ ๐๐ข๐๐ซ๐๐ซ๐๐ก๐ข๐๐ฌ
Whether it's org charts or product categories, not all data is flat. Learn how to join a table to itself or use recursive CTEs to navigate parent-child relationships effectively.
You donโt need to memorize 100 functions. You need to understand 10 really well and apply them smartly. These are the concepts I keep going back to not just in interviews, but in the real world where clarity, performance, and logic matter most.
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