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_87 ( market_value__us INTEGER, rank VARCHAR, revenues__us$_billion_ VARCHAR, company VARCHAR )

### Question ###
What is the average market value with a revenue greater than 6.2, a Company of national bank of greece, and a Rank smaller than 1?

### Accurate SQL ###

SELECT AVG(market_value__us) AS $_billion_ FROM table_name_87 WHERE revenues__us$_billion_ > 6.2 AND company = "national bank of greece" AND rank < 1