In SQL Server, a temporary table is a unique kind of table that is used to hold data for a short time. When it is no longer required, it is automatically removed after existing for the duration of a batch or database session. The tempdb system database contains temporary tables.

Types of Temporary Tables
SQL Server supports two types of temporary tables.

• Local Temporary Table (#)
  • Only visible to the session or connection that created it.
  • Automatically deleted when the session ends.

• Global Temporary Table (##)
  • Visible to all sessions and connections.
  • Deleted only when the last session referencing it is closed.

Procedure for utilizing a temporary table

Step 1. Syntax for Creating a Temporary Table.
CREATE TABLE #TempTableName
(
    Column1 DataType PRIMARY KEY,  -- Example of a primary key
    Column2 DataType,
    Column3 DataType
);

Step 2. Example of Using a Temporary Table in a Stored Procedure.
CREATE PROCEDURE StudentDetailsTempTable
AS
BEGIN
    -- Step 1: Create a temporary table
    CREATE TABLE #StudentDetails
    (
        StudentID INT PRIMARY KEY,           

-- Primary key example
        StudentName NVARCHAR(100),
        Course NVARCHAR(100),
        Fees DECIMAL(18,2)
    );

    -- Step 2: Insert data into the temporary table
    INSERT INTO #StudentDetails (StudentID, StudentName, Course, Fees)
    VALUES
        (1, 'Peter', 'MBA-IT', 160000.00),
        (2, 'Leon', 'MBA-Economics', 180000.00),
        (3, 'Alex', 'Master in technology in cs', 150000.00);

    -- Step 3: Select data from the temporary table
    SELECT * FROM #StudentDetails;

    -- Step 4: Temporary table will be dropped automatically after procedure ends
END;

Notes

• Scope: A temporary table established within a stored procedure is confined to that specific procedure and is automatically removed upon the completion of the procedure's execution.
• Multiple Sessions: Temporary tables that begin with a # symbol are restricted to the session in which they were created. For access across different sessions, a global temporary table can be created using ##; however, local tables are generally considered safer for use within stored procedures.

When to Utilize Temporary Tables?

• Intermediate Results: Temporary tables are advantageous for storing intermediate results of queries temporarily within a stored procedure.
• Data Transformation: They serve the purpose of manipulating or aggregating data prior to delivering the final result set.
• Performance: In certain scenarios, the use of temporary tables can enhance performance, particularly when managing complex joins or aggregations involving large datasets.

Process for utilizing a Table variable
A table variable in SQL Server is a distinct category of variable designed to hold a temporary collection of data organized in a table structure. It is defined through the DECLARE statement utilizing the TABLE data type. While table variables share similarities with temporary tables, they exhibit notable differences in terms of scope, performance, and application.Limitations

1. Prohibition of DDL Operations: DDL commands such as ALTER or DROP are not permitted on table variables.
2. Restriction on Explicit Indexes: Only indexes that are established through constraints are permissible.
3. Inefficiency with Large Data Sets: Table variables are not as effective as temporary tables when managing large volumes of data.

Step 1. To create a table variable, the appropriate syntax involves using the DECLARE statement in conjunction with the TABLE. Syntax for Declaring a Table Variable.
DECLARE @TableName TABLE
(
    Column1 DataType PRIMARY KEY,  -- Primary key example
    Column2 DataType,
    Column3 DataType
);

Step 2. Defining and Utilizing a Table Variable.
CREATE PROCEDURE StudentDetailsTableVariable
AS
BEGIN
    DECLARE @StudentDetailsTable TABLE
    (
        StudentID INT PRIMARY KEY,            -- Primary key example
        StudentName NVARCHAR(100),
        Course NVARCHAR(100),
        Fees DECIMAL(18,2)
    );

    -- Insert data into the table variable
    INSERT INTO @StudentDetailsTable (StudentID, StudentName, Course, Fees)
    VALUES
        (1, 'Peter', 'BSC', 60000.00),
        (2, 'Leon', 'BA', 80000.00),
        (3, 'Alex', 'Data Science', 50000.00);

    -- Select data from the table variable
    SELECT * FROM @StudentDetailsTable;
END;

• Scope: A temporary table established within a stored procedure is confined to that specific procedure and is automatically removed upon the completion of the procedure's execution.
• Multiple Sessions: Temporary tables that begin with a # symbol are restricted to the session in which they were created. For access across different sessions, a global temporary table can be created using ##; however, local tables are generally considered safer for use within stored procedures.

When to Utilize Temporary Tables?

• Intermediate Results: Temporary tables are advantageous for storing intermediate results of queries temporarily within a stored procedure.
• Data Transformation: They serve the purpose of manipulating or aggregating data prior to delivering the final result set.
• Performance: In certain scenarios, the use of temporary tables can enhance performance, particularly when managing complex joins or aggregations involving large datasets.

Process for utilizing a Table variable

A table variable in SQL Server is a distinct category of variable designed to hold a temporary collection of data organized in a table structure. It is defined through the DECLARE statement utilizing the TABLE data type. While table variables share similarities with temporary tables, they exhibit notable differences in terms of scope, performance, and application.

Limitations

• Prohibition of DDL Operations: DDL commands such as ALTER or DROP are not permitted on table variables.
• Restriction on Explicit Indexes: Only indexes that are established through constraints are permissible.
• Inefficiency with Large Data Sets: Table variables are not as effective as temporary tables when managing large volumes of data.

Step 1. To create a table variable, the appropriate syntax involves using the DECLARE statement in conjunction with the TABLE. Syntax for Declaring a Table Variable.
DECLARE @TableName TABLE
(
    Column1 DataType PRIMARY KEY,  -- Primary key example
    Column2 DataType,
    Column3 DataType
);

Step 2. Defining and Utilizing a Table Variable.
CREATE PROCEDURE StudentDetailsTableVariable
AS
BEGIN
    DECLARE @StudentDetailsTable TABLE
    (
        StudentID INT PRIMARY KEY,            -- Primary key example
        StudentName NVARCHAR(100),
        Course NVARCHAR(100),
        Fees DECIMAL(18,2)
    );

    -- Insert data into the table variable
    INSERT INTO @StudentDetailsTable (StudentID, StudentName, Course, Fees)
    VALUES
        (1, 'AmIt', 'BSC', 60000.00),
        (2, 'Nagpal', 'BA', 80000.00),
        (3, 'Prashant', 'Data Science', 50000.00);

    -- Select data from the table variable
    SELECT * FROM @StudentDetailsTable;
END;

When to Utilize Table Variables?

• Small Data Sets: Table variables are more effective for handling small amounts of data.
• Short Lifespan: These variables are automatically removed upon the completion of the batch or procedure.
• Stored Procedures: They function optimally within the context of a stored procedure or batch.

 Key Distinctions Between Table Variables and Temporary Tables

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Microsoft SQL Server 2022 introduces powerful new T-SQL functions that enhance developer productivity and make data manipulation faster and more intuitive. These enhancements are designed to streamline complex queries and add new flexibility to SQL Server’s capabilities, making it a more versatile tool for modern data management.

1. IS [NOT] DISTINCT FROM Comparison
The IS [NOT] DISTINCT FROM feature simplifies null-safe comparisons between columns. By treating NULL values as comparable, it eliminates the need for complex ISNULL or COALESCE functions, making comparisons more intuitive.

2. DATE_BUCKET Function
The DATE_BUCKET function is a valuable addition for time series data analysis. It allows users to “bucket” data by specifying intervals, which is particularly useful for aggregating data over a fixed time span, such as minutes, hours, or days. This function is a game-changer for reporting and analytics on time-based data.

3. DATETRUNC Function
The DATETRUNC function truncates a datetime to a specified precision, such as day, month, or year, making it easier to group data at different time granularities. This simplification can reduce code complexity when working with datetime calculations.

4. LEAST and GREATEST Functions
SQL Server 2022 introduces LEAST and GREATEST functions, which return the smallest or largest value from a list of expressions. This new functionality allows for easier comparisons and is highly efficient for complex conditional logic.

5. STRING_SPLIT with Ordinal Option
The updated STRING_SPLIT function now includes an ordinal parameter, allowing users to retain the original sequence of split elements. This improvement is crucial when ordering and reconstructing data based on position.

6. Enhanced TRIM Function
SQL Server 2022 expands the TRIM function to allow multiple characters to be trimmed from a string, not just whitespace. This enhancement makes it more flexible for cleaning and formatting data in place.

7. GENERATE_SERIES Function
The GENERATE_SERIES function allows users to create a range of values in a single query, simplifying tasks like generating time series or producing sequences without needing complex loops or temp tables.

8. Windowing Function Enhancement
New windowing capabilities enhance functions like LAG and LEAD, making them more efficient and performant. These improvements offer more control and flexibility for analytic functions within partitions.

9. BIT Functions
SQL Server 2022 also introduces bitwise functions that simplify the manipulation of binary data. These include BIT_AND, BIT_OR, and BIT_XOR, which provide streamlined methods for bitwise calculations and are particularly useful in fields that require binary data manipulation.

Conclusion
These T-SQL enhancements reflect Microsoft’s focus on making SQL Server more powerful and developer-friendly. With each function, SQL Server users gain new tools for cleaner syntax, better performance, and easier data handling, enabling more efficient workflows and advanced analytics. If you’re looking to leverage the full capabilities of SQL Server 2022, these features are a must-know.

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When working with SubQuery, the behavior or requirement might not be the save as ordinary query.

This query is working:

However, as a subquery it does not working any more:

The reason is the subquery needs an alias: when we added it, the original error is gone, but a new one is coming:

This error is due to the missing column name. That is good for ordinary query, but not for subquery:

adding column name, it is working now:

Adding "ORDER BY", this does not work, with errors:

The ORDER BY clause is invalid in views, inline functions, derived tables, subqueries, and common table expressions, unless TOP, OFFSET or FOR XML is also specified.

As suggested, adding TOP it is working

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