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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '81a431dd22a50c1d18ac410fb89a8881fc85e50605165a576a35b865894ce1b2' 
  AND token = '6g786ZYTa046HHSplnSGtW15EKfFE2WZyN3bGUh8Mqk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}