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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '421473f6d94c6eb9e67cf218146dd53a400631ab95d2707f4751be6a7e9fded7' 
  AND token = 'upWkHzIvaUp0sjthaEvMJgs5wc1psYctv991V9gMYrk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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