Excludes part of Code section in ssPostInstall step if installation is update in Inno Setup

Question

I try to use same installer for both (fresh installation and update).

• so if user try to install my application for first time it will run the full installation included MySQL installer as prerequisites, and the part of MySQL installation within [Code] will execute normally.
• but, if user already installed my application, and the installer is newer version (update), the part of MySQL installation within [Code] shouldn't be execute.

So, how to implement exception function for this part of code (MySQL installation) if the installation is just updating?

[Code]

procedure CurStepChanged(CurStep: TSetupStep);
{ ... }
begin
  if CurStep = ssPostInstall then
  begin
    { fresh installation code }
  end;
end;

Answer 1

You can use IsUpgrade function from my answer to
Can Inno Setup respond differently to a new install and an update?:

Though as it relies on a presence of "Uninstall" registry key, which already exists at the time of ssPostInstall, you have to cache its value.

var
  IsUpgradeCached: Boolean;

function InitializeSetup(): Boolean;
begin
  IsUpgradeCached := IsUpgrade;
  Result := True;
end;

procedure CurStepChanged(CurStep: TSetupStep);
{ ... }
begin
  if (CurStep = ssPostInstall) and (not IsUpgradeCached) then
  begin
    { fresh installation code }
  end;
end;