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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'af12b26d204d503875c11e297e4e5d95c958304fe93dcf36306ed610bbc69d73' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

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