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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b4fb51dbffc38bdbe48aedaa11dd4da176decf8f6933aa311771ca75dcec434a' 
  AND token = 'RP8UNnnBiW7iXzV9X4p6Tk+P/wJDiNmkZYkZXiz/IcQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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