Is \"IN\" Clause as Efficient as \"=\" for a Single Value in MySQL SELECT Queries?

MySQL Performance: "IN" Clause vs. Equals (=) for a Single Value

When performing SELECT queries in MySQL with a WHERE clause that filters by a single value, it is worth considering whether to use the "IN" clause or the equals (=) operator. This question explores the performance implications of using each approach.

Performance Comparison

To determine the performance impact, we can analyze the results of an EXPLAIN statement on queries with both the "IN" clause and the equals operator. Here are the results:

• Query with "=" 1:

  • EXPLAIN output shows an index scan on the "id" column.

• Query with "IN"(1):

  • EXPLAIN output shows an index scan on the "id" column.

• Query with "IN"(1,2,3):

  • EXPLAIN output shows a range scan on the "id" column.

Based on these results, we can conclude that MySQL optimizes the "IN" clause with a single value to perform the same as an equals comparison. Specifically, it uses an index scan rather than a range scan, resulting in improved performance.

Conclusion

For queries with a WHERE clause that filters by a single value, both the "IN" clause and the equals operator will perform similarly. MySQL optimizes the "IN" clause to behave like an equals comparison, providing the same level of performance. Therefore, in most cases, it is not necessary to perform the additional check to determine whether the number of values in the list is 1, as the performance difference is negligible.

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