In[]:=
d1=Dataset[{​​<|"a"1,"b""x","c"{1}|>,​​<|"a"2,"b""y","c"{2,3}|>,​​<|"a"3,"b""z","c"{3}|>​​}]​​d2=Dataset[{​​<|"a"4,"b""x","c"{4,5}|>,​​<|"a"5,"b""y","c"{5,6,7}|>,​​<|"a"6,"b""z","c"{}|>}]​​t=Join[Normal/@{d1,d2}]//Dataset
Out[]=
a
b
c
1
x
{1}
2
y
{2,3}
3
z
{3}
Out[]=
a
b
c
4
x
{4,5}
5
y
{5,6,7}
6
z
{}
Out[]=
a
b
c
1
x
{1}
2
y
{2,3}
3
z
{3}
4
x
{4,5}
5
y
{5,6,7}
6
z
{}