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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'e7c9ba38830c3a5262d405b9d3e3068633a2e58724d39e7163b6293b2d387a7d' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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