What is the process of assigning variables in Postgres SQL?

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In Postgres SQL, variables are assigned using the "SET" command. The general syntax for assigning variables is as follows:

SET variable_name = value;

For example, to assign a variable named "num" and set its value to 10, the command would be:

SET num = 10;

Note that variables in Postgres SQL are prefixed with a dollar sign ($), so the variable name in the command above would actually be "$num". Once the variable has been assigned, it can be used in subsequent SQL statements by enclosing it in dollar signs, like so:

SELECT * FROM mytable WHERE column = $num;

This would return all rows from the table "mytable" where the value in the "column" column matches the value of the "num" variable.