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COALESCE() is not a method in Python, but a function in SQL.

In SQL, the COALESCE() function is used to return the first non-null expression in a list of expressions. It takes a series of arguments and returns the first non-null value.

For example, if you have a table with two columns, "name" and "nickname", and you want to select a single column that contains either the nickname or the name if the nickname is null, you can use the following SQL statement:

SELECT COALESCE(nickname, name) AS displayname FROM tablename;

This will return a single column called "display_name" that contains the nickname if it's not null, or the name if the nickname is null.

In Python, you can use a similar function called "if None" to return a default value if a variable is null:

display_name = nickname if nickname is not None else name

This will set the "display_name" variable to the value of "nickname" if it's not null, or to the value of "name" if the "nickname" variable is null.