What is the difference between INSERT INTO and INSERT INTO SELECT in SQL?

 In SQL, both INSERT INTO and INSERT INTO SELECT are used to insert data into a table, but they serve different purposes and have distinct use cases.

Here's the difference between the two:

1. INSERT INTO:

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   • INSERT INTO is used to insert explicit values into a table, allowing you to specify the values for each column explicitly.

   • It is commonly used when you want to add new records to a table with specific values.

   • You provide the values directly in the VALUES clause.

   • Example:

     INSERT INTO customers (first_name, last_name, email)
     VALUES ('John', 'Doe', 'john.doe@example.com');
     

   • This statement inserts a new customer with the specified first name, last name, and email into the "customers" table.

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2. INSERT INTO SELECT:

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   • INSERT INTO SELECT is used to insert data into a table by selecting data from another table. It copies data from an existing table and inserts it into the specified table.

   • It is often used when you want to copy data from one table into another or consolidate data from multiple tables.

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   • Instead of specifying values directly, you specify a SELECT query that retrieves the data you want to insert.

   • Example:

     INSERT INTO new_customers (first_name, last_name, email)
     SELECT first_name, last_name, email
     FROM old_customers
     WHERE registration_date > '2022-01-01';
     

   • This statement inserts data into the "new_customers" table by selecting specific columns from the "old_customers" table for records meeting the condition.

In summary, the key difference between INSERT INTO and INSERT INTO SELECT is that the former inserts explicit values into a table, while the latter copies data from one or more existing tables into the target table. INSERT INTO SELECT is a powerful tool for data migration, data consolidation, and creating new tables with data derived from existing ones.