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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c05e12ea68f4f5f9d2b1d812f0f03bc4fbb6601b82ef1a00900422e3bbc06032' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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