Cleaning up the syntax of SQL strings

There is a mixture of string compilations in exposure-lib that sometimes makes reading the strings difficult. We initially used

sql_statement = "SELECT ..."
sql_statement += "FROM ..."

and later

sql_statement = """
    SELECT ...
    FROM ...
    """

The latter option produces much better readable code and I suggest to change to this type of string compilations (preferably using the f-string syntax).

Another aspect to change could be renaming sql_statement to sql to keep the code shorter.

\rfc @tara @laurens