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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'f6b8cb0897a7e47a99aeabf9339a7a7a8a123c06ffd875f8fcc0a679a267ddfe' 
  AND token = 'kxJFYmQpiuRHV/EwFkmVVXJ3FoV/VLoM5vLs+AwqzME=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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