Help with data appending to a file

Shell Programming and Scripting
1

Hi
I have a file called text.txt contains

x
y
z

when i run a command i will get output like below

x 20 
z 30

i want to insert x, z value in text.txt file and should be like this

x 20
y 0
z 30

can anyone help me please?

2 
# cat file1
x
y
z
# cat file2
x 20
z 30
# join -a1 -o 0 2.2 -e 0 file1 file2
x 20
y 0
z 30