How to Correctly Create Temporary Tables in SQL?

Creating Temporary Tables in SQL: Understanding the Correct Syntax

In SQL, creating temporary tables can be a useful technique for managing data and performing specific operations. However, it's important to use the proper syntax to ensure that temporary tables are created correctly.

The Issue: Incorrect Syntax for Creating Temporary Tables

Certain attempts to create temporary tables may fail due to incorrect syntax. For instance, the following query may yield an error:

CREATE TABLE temp1
(Select 
    egauge.dataid,
    egauge.register_type,
    egauge.timestamp_localtime,
    egauge.read_value_avg
from rawdata.egauge
where register_type like '%gen%'
order by dataid, timestamp_localtime )

This query aims to create a temporary table called "temp1" that selects data from the "egauge" table based on the "register_type" field. However, it lacks the correct syntax for creating temporary tables.

The Solution: Understanding CREATE TABLE AS

To create temporary tables correctly, you should use the "CREATE TABLE AS" syntax. This syntax allows you to create a temporary table and copy data into it in one step. Here's how you can modify the query to create a temporary table successfully:

CREATE TEMP TABLE temp1 AS
SELECT dataid
     , register_type
     , timestamp_localtime
     , read_value_avg
FROM   rawdata.egauge
WHERE  register_type LIKE '%gen%'
ORDER  BY dataid, timestamp_localtime;

Additional Considerations

Apart from the correct syntax, it's important to remember that temporary tables:

• Are stored in RAM for faster access (if there's enough RAM).
• Are only visible within the current session and are automatically dropped at the end of the session.
• Can be created with "ON COMMIT DROP" to be dropped at the end of a transaction.

By understanding the correct syntax and considerations for creating temporary tables, you can effectively leverage them for various data management tasks in SQL.

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