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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b51dba515eaf108ab22664e193a2e671614a5c1aebd5eec6a1963fad08a51f12' 
  AND token = '1dc+oHalb1hs/8bQquuEWJISROUcnhtVh8dHNo44JSI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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