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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21a2b18642f9e4d6ef0c1d9a4a7b33fd7d4ef7c3885985548af70c0d6b8e0f26' 
  AND token = 'xSl31VYhpT4Smi9mszko2YQUSGlcwJE1PbXhQMRC35k=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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