5 Ways Select Into Temp Table

Selecting data into a temporary table is a common operation in SQL, allowing for the manipulation and analysis of data in a temporary storage space. This process is particularly useful in complex queries where intermediate results need to be stored for further processing. Here, we'll explore five ways to select data into a temporary table, each with its own advantages and use cases.

1. Using Select Into Statement

The SELECT INTO statement is the most straightforward way to create a temporary table and populate it with data in a single step. This method is particularly useful when you need to create a new table based on the result of a query. The syntax is as follows:

SELECT column1, column2
INTO #TempTable
FROM SourceTable;

This method creates a new temporary table named `#TempTable` and inserts the data from `SourceTable` into it. Note that the temporary table is created in the `tempdb` database and is automatically dropped when the session is closed.

Advantages and Limitations

The SELECT INTO statement is simple and efficient but offers limited control over the structure of the temporary table. Additionally, if the temporary table already exists, this statement will fail, requiring you to drop the table before running the statement again.

2. Using Insert Into Statement

The INSERT INTO statement allows you to insert data into an existing temporary table. This method provides more flexibility than SELECT INTO because you can create the temporary table with specific data types and constraints before inserting the data.

CREATE TABLE #TempTable (
    column1 INT,
    column2 VARCHAR(50)
);

INSERT INTO #TempTable (column1, column2)
SELECT column1, column2
FROM SourceTable;

This approach gives you full control over the temporary table's structure and allows for the insertion of data from various sources.

Flexibility and Control

The INSERT INTO method is more flexible than SELECT INTO because it allows for the creation of the temporary table before data insertion, enabling the specification of data types, constraints, and indexes.

3. Using Create Table Statement

The CREATE TABLE statement followed by an INSERT INTO statement offers even more control over the temporary table’s structure. This method is similar to the INSERT INTO statement but emphasizes the separate creation of the table before data insertion.

CREATE TABLE #TempTable (
    column1 INT PRIMARY KEY,
    column2 VARCHAR(50) NOT NULL
);

INSERT INTO #TempTable (column1, column2)
SELECT column1, column2
FROM SourceTable;

This approach is useful when you need to specify primary keys, foreign keys, or other constraints on the temporary table.

Table Structure Customization

By separating the creation and population of the temporary table, you can customize the table’s structure to fit your specific needs, including the addition of constraints and indexes.

4. Using CTAS (Create Table As Select)

The CTAS method is similar to the SELECT INTO statement but is used in different database systems. The syntax might vary slightly depending on the database management system you are using.

CREATE TABLE TempTable AS
SELECT column1, column2
FROM SourceTable;

This method creates a new permanent table based on the result of a query, which can then be used as needed.

Permanent Table Creation

The CTAS method is useful when you need to create a permanent table based on query results, offering a straightforward way to do so.

5. Using Temporary Table Variables

Temporary table variables are used to store the result set of a query in a variable. They are declared using the DECLARE statement and can be used within the scope of a batch or stored procedure.

DECLARE @TempTable TABLE (
    column1 INT,
    column2 VARCHAR(50)
);

INSERT INTO @TempTable (column1, column2)
SELECT column1, column2
FROM SourceTable;

This method is useful for storing small result sets that need to be manipulated within a procedure or batch.

Scope and Accessibility

Temporary table variables are accessible within the scope of their declaration and offer a convenient way to store and manipulate small datasets.