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SELECT 
  * 
FROM 
  cscart_wk_delivery_day_settings 
  LEFT JOIN cscart_shippings ON cscart_shippings.shipping_id = cscart_wk_delivery_day_settings.shipping_id 
WHERE 
  1 
  AND cscart_wk_delivery_day_settings.company_id = 0 
  AND cscart_wk_delivery_day_settings.shipping_id = '6' 
  AND cscart_shippings.wk_en_delivery_time = 'Y'

Query time 0.00074

JSON explain

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