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_name_20 ( opened INTEGER, venue VARCHAR, established VARCHAR )

### Question ###
When is the earliest year opened for huff hall that was established after 1974?

### Accurate SQL ###

SELECT MIN(opened) FROM table_name_20 WHERE venue = "huff hall" AND established > 1974