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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6a27d58764ba2f926d3597a514ce6ef51f1553a3dda0accf947954cdcd9994a7' 
  AND token = 'RSLel293mKY69DID4U2ZwvofajM3uSW+CHDu5iGEjA4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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