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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '875300da57f0f5baf97bf7447dab55e25709f4b8f55644dd5f2e2c3523f857d0' 
  AND token = '6n2JVGzUVhM5AJExIdUrLXuA6hoQuRgs+1pRYb7Rq/s=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00016

JSON explain

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