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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'b7ce138849896d5d9b0256570b558e4337e1e3ec2f9e3c9eacb5167ecd12a957' 
  AND token = 'myiZcqhKBoESdXgT7TNIP8N0s6WLqb5saQGLWwwP0Z8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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