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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '9cdb3b9a27ad5977539a2e3998e634499689b8b540796196863d68a09a767c80' 
  AND token = 'r3Zht70CggasvruQDEKkyGARsdCKxmMVIy+pApVdmEk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}