Why Doesn't SQL Have a Built-in PRODUCT Aggregate Function?

The Curious Case of the Missing PRODUCT Aggregate in SQL

SQL offers various aggregate functions like SUM and AVERAGE for performing computations on groups of data. However, one function that's noticeably absent is PRODUCT, which would calculate the multiplication of values within a group.

Why the Absence?

There are several reasons why SQL may not have a PRODUCT aggregate function:

• Mathematical Challenges: Calculating the product of an arbitrary number of values in an efficient and scalable way can be computationally intensive.
• Optimization Limitations: Query optimizers often rely on statistical information about data distribution to optimize queries. Multiplying multiple values can distort statistics and make optimization challenging.
• Rare Usage: Compared to other aggregate functions like SUM or AVERAGE, PRODUCT is relatively less commonly used. Implementing it for limited usage might not justify the development effort.

Alternatives and Workarounds

Even without a dedicated PRODUCT function, there are ways to achieve multiplication operations in SQL. One approach is to use the EXP() and LOG() functions in combination. For instance:

SELECT
    GrpID,
    EXP(SUM(LOG(ABS(NULLIF(Value, 0)))))
FROM
    Mytable
GROUP BY
    GrpID;

While this provides an approximation of the product, it may not be exact due to precision limitations.

Other Examples

If you need to multiply values within a row, you can use the * operator. For example:

SELECT
    ID,
    Price * Quantity AS Total
FROM
    Sales;

In case you need to calculate the product of multiple groups or subqueries, you can use a nested query or a subquery factoring technique.

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