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_715 ( "District" text, "Incumbent" text, "Party" text, "First elected" real, "Result" text, "Candidates" text )

### Question ###
What is the minimum first elected for ed markey?

### Accurate SQL ###

SELECT MIN("First elected") FROM table_715 WHERE "Incumbent" = 'Ed Markey'