Multiple INSERT Statements or a Single INSERT with Multiple VALUES: Which Performs Better?

Multiple INSERT statements and a single INSERT statement containing multiple VALUES: performance comparison

Contrary to conventional wisdom, this test result shows that the performance of multiple INSERT statements is better than a single INSERT statement containing multiple VALUES. Although a single INSERT statement is usually more concise and appears to be more efficient, test results show that its execution speed can be ten times slower.

The performance difference arises from the compilation phase of query execution. When using a single INSERT statement that contains multiple VALUES, SQL Server attempts to compile a plan for each literal value in the VALUES clause. When the number of VALUES clauses exceeds a certain threshold, the efficiency of the compilation process decreases, resulting in an increase in compilation time and a decrease in overall performance.

In contrast, using multiple INSERT statements forces SQL Server to compile a separate plan for each INSERT statement. While this may seem less efficient in terms of code execution, it actually reduces the impact on compile time, thereby improving overall performance.

Additionally, the size of the inserted string also affects performance, with longer strings resulting in slower compile times. However, duplicates in a string have the opposite effect, improving performance due to SQL Server's ability to identify and optimize query plans.

In summary, while a single INSERT statement containing multiple VALUES may seem simpler and more efficient, using multiple INSERT statements can significantly improve performance, especially when dealing with large numbers of values ​​or long string data.

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