Task: Text to Code
Input (English): Step 1: For each row in Documents table, find the corresponding rows in Documents_Mailed table.
Step 2: find receipt_date of the results of step 1 whose Documents_Mailed's document_id equals 7
Output (English): SELECT T1.receipt_date FROM Documents AS T1 JOIN Documents_Mailed AS T2 ON T1.document_id = T2.document_id WHERE T2.document_id = 7