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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6346049f2d8ffcf7b55a0c5283afa4bdb07cf6fe21b0e49aa8e2f7a215232bec' 
  AND token = '5gAPxkM3eFxEVs4mLZBIxM25l/G9wCDVbr8eL9B/sM8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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