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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'f5b0a7c5df18f2e0f8dbc629eb4e976a0c2b0cfb1a21edb614deaddeb4650a68' 
  AND token = '/kPtwzdySeCE7bWyppi9tc4pUDQGY4L5fQ9NEb6zURg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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