In SQL, temporary tables are a useful tool for storing intermediate data that you can use within a specific session or query. The temporary table is only visible to the current user and is automatically dropped when the session ends.

Creating a Temporary Table

To create a temporary table, you can use the CREATE TEMPORARY TABLE statement followed by the table name and the column definitions. For example:

CREATE TEMPORARY TABLE temp_table (
    id INT,
    name VARCHAR(50)
);

This will create a temporary table called temp_table with two columns: id of type INT and name of type VARCHAR(50).

Populating a Temporary Table

Once the temporary table is created, you can populate it with data using INSERT INTO statements, just like you would with a regular table. For example:

INSERT INTO temp_table (id, name)
VALUES (1, 'John'),
       (2, 'Jane'),
       (3, 'Alice');

This will insert three rows into the temp_table.

Using a Temporary Table in a SELECT Statement

To use the temporary table in a SELECT statement, you can join it with other tables or use it directly in the query. For example:

SELECT t.name, other_table.column
FROM temp_table t
JOIN other_table ON t.id = other_table.id
WHERE t.id > 1;

In this example, we select the name column from the temp_table and the column from another table called other_table. We join the two tables based on the id column and filter the result to include only rows where the id is greater than 1.

Dropping a Temporary Table

As mentioned earlier, temporary tables are automatically dropped when the session ends. However, you can also explicitly drop them using the DROP TEMPORARY TABLE statement. For example:

DROP TEMPORARY TABLE temp_table;

This will remove the temporary table called temp_table.

Conclusion

Temporary tables are a powerful feature in SQL that allow you to store intermediate data within a session or query. They can greatly simplify complex queries and improve performance. Remember to use them wisely and drop them when they are no longer needed.

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