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database/notes/09-subqueries-views.md
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@ -13,6 +13,7 @@
- [Index Range scan](#index-range-scan)
- [Index seek](#index-seek)
- [Some guidelines for optimizing MySQL queries](#some-guidelines-for-optimizing-mysql-queries)
- [Practice questions](#practice-questions)
## Sub-queries
@ -223,4 +224,12 @@ This happens when you specify a condition in WHERE clause like searching an empl
* Avoid unnecessary columns in SELECT clause
Instead of using ‘SELECT *’, always specify columns in the SELECT clause to improve MySQL performance. Because unnecessary columns cause additional load on the database, slowing down its performance as well whole systematic process.
* Pagination
* Avoid SELECT DISTINCT
* Avoid SELECT DISTINCT
## Practice questions
* [Sub-queries - I](https://leetcode.com/problems/customers-who-never-order/)
* [Sub-queries - II](https://leetcode.com/problems/sales-person/)
* [Sub-queries - III](https://leetcode.com/problems/consecutive-available-seats/)
* [Sub-queries - IV](https://leetcode.com/problems/sales-analysis-ii/)
* [Sub-queries - V](https://leetcode.com/problems/students-with-invalid-departments/)
* [Sub-queries - VI](https://leetcode.com/problems/customer-who-visited-but-did-not-make-any-transactions/)