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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '876ca678cd84b4138c4948af99cc29c8fc503805c530f3ca1aaba5f97a38e04f' 
  AND token = 'Q/CzECiPG9ajYaTjvQRIiXknkE+Z0xFFP+BksyqeNic=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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