Improving the effectiveness of queries is crucial for database optimization. Common Table Expressions (CTE) and temporary tables are two alternative ways that Microsoft SQL Server can improve query performance. But the question remains: which tactic works better in terms of efficiency and speed?

Frequently Used Table Terms (CTE)
Creating temporary result sets inside of a query is made easy and clear with the help of CTEs. By dividing intricate reasoning into smaller, easier-to-understand components, they improve query readability. CTEs can be referenced more than once and are defined within the query scope, which minimizes redundancy and enhances maintainability.

This is an example CTE query:
WITH CTE_Sales AS (
    SELECT ProductID, SUM(Quantity) AS TotalSales
    FROM Sales
    GROUP BY ProductID
)
SELECT P.ProductName, S.TotalSales
FROM Products P
JOIN CTE_Sales S ON P.ProductID = S.ProductID;

In this example, CTE_Sales calculates the total sales per product, which is later joined with the Products table.

Temporary Tables
Conversely, temporary tables are made physically inside the tempdb database. They hold temporary outcomes and continue until the session is over unless they are specifically removed. Although creating temporary tables requires more resource allocation and I/O cost, there are occasions where doing so improves speed, particularly for larger datasets or more complicated procedures.

Think about the following case with temporary tables:
CREATE TABLE #TempSales (
    ProductID INT,
    TotalSales INT
);

INSERT INTO #TempSales (ProductID, TotalSales)
SELECT ProductID, SUM(Quantity) AS TotalSales
FROM Sales
GROUP BY ProductID;

SELECT P.ProductName, TS.TotalSales
FROM Products P
JOIN #TempSales TS ON P.ProductID = TS.ProductID;

DROP TABLE #TempSales;

Here, #TempSales is created to hold the total sales per product before being joined with the Products table.

Comparing Speeds
Variations exist in the performance of CTEs and temporary tables due to variables such as query complexity, indexing, and dataset size. Because CTEs are in-memory and have minimal I/O cost, they often provide equivalent or occasionally higher performance in circumstances involving smaller datasets or simpler processes.

However, temporary tables may perform better than CTEs for larger datasets or more intricate tasks requiring several steps. Indexing can help temporary tables by enabling more efficient joins and quicker data retrieval.

In summary
Depending on a number of variables, one must decide whether to optimize query time using temporary tables or CTEs. Temporary tables excel at managing larger datasets and complex procedures, particularly when indexing and multi-step computations are involved. CTEs improve readability and are useful for simpler tasks.

In the end, experimenting, profiling, and taking into account the particular context of the query and database structure are frequently necessary for query performance optimization. Producing effective SQL queries in Microsoft SQL Server requires striking a balance between readability, maintainability, and efficiency.

Recall that there are two types of tools in the SQL optimization toolbox: temporary tables and CTEs. The best tool to use will depend on the particular needs of the task at hand.

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