Extracting and interpreting data can be very valuable to an organization.
- Describe the importance of using sub queries in a database system. Provide at least two business case scenarios to support your response.
- Be sure to respond to at least one of your classmates' posts.
33 minutes ago
Giovanni Ortiz
RE: Week 8 Discussion Top of Form
Subqueries are Select queries within an INSERT, MERGE, UPDATE, or DELETE statement. The benefits of having subqueries is that it makes logical sense to read and thus makes it easier for users to understand what a query is doing. The downside to implementing subqueries in your DML's is that they take longer to execute because of the way the database optimizer works. Although a join is more efficient to use than a subquery there are specific instances when to use a subquery. The first instance we would use a subquery over a Join is when there is more than one query to return and each subquery provides a subset of the table involved in the query. Another instance where subqueries are used over queries is if you specifically have to use the NOT EXISTS or EXISTS condition which is native to only subqueries. A general rule of thumb when guessing the performance impact of running subqueries is finding out if it is an independent or dependent subquery.
Resources:
1. Bellamkonda, S., Ahmed, R., Witkowski, A., Amor, A., Zait, M., & Lin, C. C. (2009). Enhanced subquery optimizations in oracle. Proceedings of the VLDB Endowment, 2(2), 1366-1377.
2. Zuzarte, C., Pirahesh, H., Ma, W., Cheng, Q., Liu, L., & Wong, K. (2003, June). Winmagic: Subquery elimination using window aggregation. In Proceedings of the 2003 ACM SIGMOD international conference on Management of data (pp. 652-656).
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