Sharepoint - Querying a simple list with a 'User' column, using CAML

Try to use this caml:

<Where>
  <Eq>
    <FieldRef Name="Author" LookupId="True" />
    <Value Type="User">123</Value>
  </Eq>
</Where>

this also might work, but first is preferable:

<Where>
  <Eq>
    <FieldRef Name="Author" LookupId="True" />
    <Value Type="Lookup">123</Value>
  </Eq>
</Where>

and also, if you want to pass current logged user into caml query, you can use this one:

<Where>
  <Eq>
    <FieldRef Name="Author" />
    <Value Type="Integer">
      <UserID />
    </Value>
  </Eq>
</Where>

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