SELECT COUNT( a.id ) 
FROM table_1 a
LEFT JOIN table_2 b ON a.id = b.id
LEFT JOIN table_3 y ON a.foo= y.id
WHERE a.bar =1
AND a.field =3
AND b.mydate <= 1159438132
AND b.status =2
AND (
y.myfield IS NULL 
OR y.myfield !=2
)

id  select_type  table  type  possible_keys  key  key_len  ref  rows  Extra  
1 SIMPLE b ref status,mydate,id,mydate_2 status 1 const 10301 Using where 
1 SIMPLE a eq_ref PRIMARY,bar,field PRIMARY 4 database_com.b.id 1 Using where 
1 SIMPLE y eq_ref PRIMARY PRIMARY 4 database_com.a.foo 1 Using where