PostgreSQL - Select Into

The SELECT INTO statement in PostgreSQL is used to create a new table and populate it with the results of a query. The new table will have columns that match the expressions in the SELECT statement, and it gets filled with the result set of that query. Essentially, SELECT INTO creates a new table from the results of a query.

Basic Syntax:

SELECT column1, column2, ...
INTO new_table
FROM existing_table
WHERE conditions;

column1, column2, ...: Columns that you want to select and insert into the new table.
new_table: The name of the new table you want to create.
existing_table: The name of the table from which you're pulling data.
WHERE conditions: Optional conditions to filter the rows that you want to insert into the new table.

Examples:

Create a new table with all columns and rows from an existing table:
```
SELECT *
INTO employees_backup
FROM employees;
```
This would create a new table named employees_backup and copy all rows and columns from the employees table into it.
Create a new table with specific columns:
```
SELECT first_name, last_name
INTO employee_names
FROM employees;
```
This would create a new table named employee_names and insert the first_name and last_name columns from the employees table.
Create a new table with rows based on a condition:
```
SELECT *
INTO hr_employees
FROM employees
WHERE department = 'HR';
```
This would create a new table named hr_employees and copy all rows from the employees table where the department is 'HR'.

Notes:

The SELECT INTO statement creates a new table without any constraints, indexes, defaults, or other properties of the original table. If you need those, you'll have to define them manually on the new table.
The new table created with SELECT INTO is a regular table, so it persists beyond the session. If you want a temporary table, you might use the CREATE TEMP TABLE or CREATE TEMPORARY TABLE commands.
Another similar command in PostgreSQL is CREATE TABLE AS, which offers functionality akin to SELECT INTO.
In some SQL databases, the syntax and behavior of SELECT INTO might differ. For example, in SQL Server, SELECT INTO is used for both creating a new table and inserting data into an existing table.

In PostgreSQL, the SELECT INTO command is handy when you need to quickly create a new table based on the results of a SELECT query.