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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'edf425fdec0581e8656721e2d1bbf82466e2b8d0d5d97a2a3c51d1c368343dd6' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

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