SELECT [Account ID] AS [Account ID], [Created Date Backend] AS [Created Date]
FROM [DE A]  A
INNER JOIN [DE B] B
WHERE A.[Account ID] = B.[Lead ID]

SELECT
[Account ID] AS 'Account ID'
,[Created Date Backend] AS 'Created Date'
FROM [DE A] A
INNER JOIN [DE B] B ON A.[Account ID] = B.[Lead ID]