-- EMPTY SET
SELECT
  *
FROM
  context AS c 
  JOIN pseudoana AS pa ON c.id_ana = pa.id 
WHERE
  c.id_report = 1
ORDER BY  c.id_ana, c.datetime
;

-- NOT EMPTY
SELECT
  *
FROM
  context AS c 
  STRAIGHT_JOIN pseudoana AS pa ON c.id_ana = pa.id 
WHERE
  c.id_report=1 AND 
  c.datetime >= '1001-01-01 00:00:00' 
ORDER BY  c.id_ana, c.datetime
;