Why is SELECT * Considered Harmful in Database Queries?

*The Downsides of Using SELECT in SQL Queries**

While seemingly simple, the widespread use of SELECT * in SQL queries can significantly impact performance and application stability. Let's examine the key drawbacks:

1. Inefficient Data Transfer: Retrieving all columns with SELECT * often includes unnecessary data. This results in increased network traffic and processing overhead, especially problematic with large datasets or slow connections. Adding columns to the underlying table further exacerbates this issue.

2. Indexing Challenges and Optimization: Effective indexing is crucial for query speed. SELECT * hinders optimal index creation because indexes are designed for specific columns. Adding or altering columns can render existing indexes less effective, slowing down queries.

3. Data Binding Issues and Maintenance: Using SELECT * can create ambiguity when joining tables with identically named columns. This can lead to data binding errors and application failures. Furthermore, changes to table structures can break views or stored procedures that rely on SELECT *.

*Situations Where SELECT Might Be Acceptable:**

Despite the general cautions, there are limited scenarios where SELECT * might be suitable:

1. Initial Data Exploration and Troubleshooting: For quick checks of table contents, especially when column names are unknown or complex, SELECT * can offer a rapid overview.

2. Simple Row Counts or Existence Checks: When the goal is merely to determine the number of rows or if rows exist, SELECT * is acceptable, as the focus is on the row count, not specific column values.

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