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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '3be4de3973266807e0b2fd241fca13dec91709966089b0aa4b59ae762125b206' 
  AND token = '6+FrmRrdjuuTqKUWDzE+tm4++WBzYEHYbmNgRjtISJo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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