SELECT 
  p.product_id, 
  ifnull(
    count(dp.post_id), 
    0
  ) as discussion_amount_posts 
FROM 
  cscart_discussion 
  INNER JOIN cscart_products as p ON (
    cscart_discussion.object_id = p.product_id
  ) 
  INNER JOIN cscart_discussion_posts as dp ON (
    cscart_discussion.thread_id = dp.thread_id 
    AND cscart_discussion.object_type = 'P' 
    AND cscart_discussion.company_id = 1
  ) 
WHERE 
  dp.status = 'A' 
  and p.product_id in (
    370, 5473, 1843, 1841, 1840, 486, 3844, 
    1842, 3854, 3853, 3852, 3851, 3850, 
    3849, 3848, 3847, 3846, 3845, 3843, 
    3856, 3785, 3841, 3840, 3839, 3838, 
    3837, 3836, 3835, 3834, 3833, 3832, 
    3855, 3857, 3830, 3801, 3882, 3881, 
    3880, 3806, 3805, 3877, 3808, 3807, 
    3874, 3873, 3812, 3870, 3815, 3814, 
    3813, 3867, 3866, 3865, 3864, 3863, 
    3862, 3861, 3824, 3859, 3831, 3829, 
    3773, 3786, 3797, 3796, 3795, 3794, 
    3793, 3792, 3791, 3790, 3789, 3788, 
    3787, 3842, 3799, 3782, 3781, 3780, 
    3779, 3778, 3777, 3776, 3775, 3774, 
    3798, 3800, 3828, 3860, 3827, 3858, 
    3823, 3822, 3821, 3820, 3819, 3818, 
    3817, 3816, 3869, 3868, 3872, 3871, 
    3811, 3810, 3809, 3876, 3875, 3879, 
    3878, 3804, 3803, 3802, 3883, 3884
  ) 
GROUP BY 
  p.product_id

Query time 0.00039

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}