Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_30759 ( "No in. series" real, "No in. season" real, "Title" text, "Original air date" text, "Production Code" real, "U.S. viewers (millions)" text )

### Question ###
What is the highest production code of the episodes having a US viewership of exactly 2.3?

### Accurate SQL ###

SELECT MAX("Production Code") FROM table_30759 WHERE "U.S. viewers (millions)" = '2.3'