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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'f8d753d60c3c8bf4f4740b69453b2e833628cf1d1f82c996282f16675b61b896' 
  AND token = '9xt679CzXwbhs8bBOFdm6rwea+WSS2ozLEWhgIUSyog=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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