How sum in sql is calculated

SQL SUM function calculates the sum of a set of numbers by adding them together. The operation process includes: 1. Identifying the input value; 2. Looping the input value and converting it into a number; 3. Adding each number to accumulate a sum; 4. Returning the sum result.

Operation of SUM function in SQL

The SUM function is used in SQL to calculate the sum of a set of numbers. Aggregation functions. It performs an addition operation on a set of values, returning a single numeric result.

Operation process

The operation process of the SUM function is as follows:

1. Identify the input value: The SUM function accepts a or multiple input values, which can be numbers, numeric expressions, or columns containing numeric values.
2. Loop input values: The function iterates through the input values ​​row by row and converts them into numbers.
3. Perform addition operations: The function adds each number and accumulates a total.
4. Return result: When all input values ​​have been processed, the function returns the sum result.

Usage Example

The following example demonstrates how to use the SUM function to calculate the sum of a set of numbers:

<code class="sql">SELECT SUM(sales)
FROM sales_table;</code>

In this example, SUM The function calculates the sum of all values ​​in the sales column in the sales_table table.

Notes

• Null value processing: The SUM function ignores null values ​​(NULL).
• Data type: The SUM function can handle numeric inputs of different data types, including integers, floating point numbers, and decimals.
• Negative values: The SUM function also sums negative values, which may result in a negative sum.

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