Why are my SQL sum calculations incorrect when combining multiple tables, and how can I fix them using subqueries?

Combining Data from Multiple Tables for Summation: Addressing Incorrect Results

In your SQL query, you aim to retrieve a table consisting of three columns: "PROJECT," "SUM_AP," and "SUM_INV." However, you have encountered incorrect results due to grouping in the aggregation process.

Cause of Incorrect Results:

The "GROUP BY" clause in your query combines values based on the "AP.[PROJECT]" column. This aggregation process essentially sums up duplicate "Value" entries, leading to inflated results.

Solution: Using Sub-Select Queries

To address this issue, we can modify your query using sub-select queries:

SELECT 
    AP1.[PROJECT],
    (SELECT SUM(AP2.Value) FROM AP AS AP2 WHERE AP2.PROJECT = AP1.PROJECT) AS SUM_AP,
    (SELECT SUM(INV2.Value) FROM INV AS INV2 WHERE INV2.PROJECT = AP1.PROJECT) AS SUM_INV
FROM 
    AP AS AP1 
    INNER JOIN INV AS INV1 
        ON (AP1.[PROJECT] =INV1.[PROJECT])
WHERE 
    AP1.[PROJECT] = 'XXXXX'
GROUP BY 
    AP1.[PROJECT]

Explanation:

• The sub-queries within the SUM() functions calculate the sums of "Value" entries from the "AP" and "INV" tables, respectively, for each unique "PROJECT" value.
• The primary query then joins these sub-queries, based on the matching "PROJECT" values, and aggregates the results once more to produce the final table.

This revised query ensures that only distinct "PROJECT" values are grouped, and the sums are calculated correctly, providing the intended result.

The above is the detailed content of Why are my SQL sum calculations incorrect when combining multiple tables, and how can I fix them using subqueries?. For more information, please follow other related articles on the PHP Chinese website!