Question

有两个表T1和T2。它们都有3列，其中2列相同，两个表中的数据相同。让它们成为T1中的ID，C1，C2和T2表中的C1，C2，COM。

事实是T2中存在所有C1数据，但可能错过C2数据。

我需要为每个ID返回一个包含COM的表。

尝试

class UserUpdateView(UpdateView):
    model = get_user_model()
    form_class = forms.UserUpdateForm

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        if self.request.POST:
            context['projectmembership_formset'] = forms.UserProjectMembershipFormSet(
                self.request.POST,
                instance=self.object
            )
        else:
            context['projectmembership_formset'] = forms.UserProjectMembershipFormSet(
                instance=self.object
            )
        return context

    def form_valid(self, form):
        '''Handle saving of the project membership formset
        '''
        context = self.get_context_data()
        project_memberships = context['projectmembership_formset']
        if project_memberships.is_valid():
            self.object = form.save()
            project_memberships.instance = self.object
            project_memberships.save()
            return super().form_valid(form)
        else:
            return self.render_to_response(self.get_context_data(form=form))

但它返回的结果不正确。

Answer 1

总结如下：您需要一个且只有一个COM ID（即使它不存在于第二个表中），并且您希望ID按升序排序。

您需要添加连接条件：

SELECT CAST(T1.ID as UNSIGNED) as ID, T2.COM
FROM T1 
LEFT JOIN T2 ON T1.C1 = T2.C1
AND (T1.C2 = T2.C2)  -- The first condition of this row is to handle the null value
OR (T1.C2 NOT IN (SELECT C2 FROM T2) AND T2.C2 = 'NA')
    ORDER BY CAST(T1.ID as UNSIGNED) -- To convert to int and sort ascending

编辑：要对结果进行升序排序，您需要将ID转换为整数，然后对结果进行排序。这是一些documentation。

Edit2：这是3和4，这是我认为更好的方法，但我不建议通常这样做

使用相同的列连接两个表

1 个答案: