Amorcer SQL Express à partir de WiX ?

Voici ce que j'ai, j'espère que cela vous aidera :

<?define ServerInstall="SomeCondition" ?>

<?define InstanceName = "YOUR_INSTANCE" ?>
<?define SqlWebLink = http://download.microsoft.com/download/5/2/9/529FEF7B-2EFB-439E-A2D1-A1533227CD69/SQLEXPR_x86_ENU.exe ?>

<Variable Name="SqlVariable" Type="string" Value="/SAPWD=some_password" Hidden="yes" />

<!-- Read SQL Server keys to find current instance and version -->
<util:RegistrySearch
  Id="SqlInstanceKeyFound"
  Root="HKLM" Key="SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL" Value="$(var.InstanceName)"
  Result="exists" Variable="SqlInstanceKeyFound" />
<util:RegistrySearch
  Id="SqlInstanceKey"
  Root="HKLM" Key="SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL" Value="$(var.InstanceName)"
  Variable="SqlInstanceKey" After="SqlInstanceKeyFound" Condition="SqlInstanceKeyFound" />
<util:RegistrySearch
  Id="SqlInstanceFound"
  Root="HKLM" Key="SOFTWARE\Microsoft\Microsoft SQL Server\[SqlInstanceKey]"
  Result="exists" Variable="SqlInstanceFound" After="SqlInstanceKey" Condition="SqlInstanceKeyFound" />
<util:RegistrySearch
  Id="SqlVersion"
  Root="HKLM" Key="SOFTWARE\Microsoft\Microsoft SQL Server\[SqlInstanceKey]\Setup" Value="Version"
  Variable="SqlVersion" After="SqlInstanceKey" Condition="SqlInstanceFound" />

<PackageGroup Id="Sql2012Express">
  <!--
    SQL Server 2012 Express - Install new instance
    http://msdn.microsoft.com/en-us/library/ms144259.aspx
    SQL Server Express requires WIndows Installer 4.5
    RepairCommand="/ACTION=Repair /INSTANCENAME=$(var.InstanceName) /Q /HIDECONSOLE"
  -->
  <ExePackage Id="Sql2012Express"
    DisplayName="SQL Server 2012 Express"
    Cache="yes"
    Compressed="no"
    PerMachine="yes"
    Permanent="no"
    Vital="yes"
    Name="Redist\SQLEXPR_x86_ENU.exe"
    SourceFile="..\Packages\SQLEXPR_x86_ENU.exe"
    DownloadUrl="$(var.SqlWebLink)"
    InstallCommand="/ACTION=Install /INSTANCENAME=$(var.InstanceName) /FEATURES=SQL /SECURITYMODE=SQL [SqlVariable] /TCPENABLED=1 /SQLSVCACCOUNT=&quot;NT AUTHORITY\NETWORK SERVICE&quot; /SQLSVCSTARTUPTYPE=Manual /SQLSYSADMINACCOUNTS=BUILTIN\Administrators /ADDCURRENTUSERASSQLADMIN=FALSE /Q /HIDECONSOLE /SkipRules=RebootRequiredCheck /IAcceptSQLServerLicenseTerms"
    UninstallCommand="/Action=Uninstall /INSTANCENAME=$(var.InstanceName) /FEATURES=SQL /Q /HIDECONSOLE"
    DetectCondition="SqlInstanceFound"
    InstallCondition="$(var.ServerInstall)">
    <ExitCode Value ="3010" Behavior="forceReboot" />
    <dep:Provides DisplayName="Net2 SQL Server 2012 Express" Key="SQLServer2012Express,$(var.InstanceName)" Version="11.0.3000.0" />
  </ExePackage>

  <!--
    SQL Server 2012 Express - Upgrade existing pre-SQL 2012 instance
  -->
  <ExePackage Id="Sql2012ExpressUpgrade"
    DisplayName="SQL Server 2012 Express Upgrade"
    Cache="no"
    Compressed="no"
    PerMachine="yes"
    Permanent="yes"
    Vital="yes"
    Name="Redist\SQLEXPR_x86_ENU.exe"
    SourceFile="..\Packages\SQLEXPR_x86_ENU.exe"
    DownloadUrl="$(var.SqlWebLink)"
    InstallCommand="/ACTION=Upgrade /INSTANCENAME=$(var.InstanceName) /Q /HIDECONSOLE /SkipRules=RebootRequiredCheck /IAcceptSQLServerLicenseTerms"
    DetectCondition="NOT (SqlInstanceFound AND (SqlVersion &lt; v11.0.0.0))"
    InstallCondition="$(var.ServerInstall)">
    <ExitCode Value ="3010" Behavior="forceReboot" />
  </ExePackage>

  <!--
    SQL Server 2012 SP1 Express - Upgrade existing SQL 2012 instance to SP1
  -->
  <ExePackage Id="Sql2012ExpressEditionUpgrade"
    DisplayName="SQL Server 2012 SP1 Express Patch"
    Cache="no"
    Compressed="no"
    PerMachine="yes"
    Permanent="yes"
    Vital="yes"
    Name="Redist\SQLEXPR_x86_ENU.exe"
    SourceFile="..\Packages\SQLEXPR_x86_ENU.exe"
    DownloadUrl="$(var.SqlWebLink)"
    InstallCommand="/ACTION=Patch /INSTANCENAME=$(var.InstanceName) /Q /HIDECONSOLE /SkipRules=RebootRequiredCheck /IAcceptSQLServerLicenseTerms"
    DetectCondition="NOT (SqlInstanceFound AND (SqlVersion &gt; v11.0.0.0) AND (SqlVersion &lt; v11.0.3000.0))"
    InstallCondition="$(var.ServerInstall)">
    <ExitCode Value ="3010" Behavior="forceReboot" />
  </ExePackage>

Vous devrez modifier les commandes d'installation pour qu'elles correspondent à vos besoins.