Difference in difference analysis

[Samuel baker]

Dear Stata forum, I am fairly new to STATA but am trying to carry out a DID analysis. I have watched some videos on Youtube and read the manual but still cannot fully understand how to set up the dataset. For context, I have carried out an experiment on campus for a class project over a period of two months. The aim of the project is to decrease the consumption of beef products. I have 1 control group (a cafe) and a treatment group (another cafe). I have data before and during the treatment. My variables include time (of the day), date, quantity of beef products sold. See below an example as to how I have coded the data so far:
Date Treatment Cafe Quantitybeef
0...........0............ 0........... 21
0.......... 0............ 0........... 25
1...........0............ 0........... etc
1...........0............ 0
0.......... 0............ 1
0...........0............ 1
1...........1.............1
1...........1.............1

I have used the stata command: didregress (Quantitybeef) (Treatment), group(Café) time(Date). However I am getting some strange results. Please could you provide some feedback on the best way to carry out a DID analysis in STATA given my context? Note, I have also tried carrying out the following code: reg Quantitybeef Treatment##Date.
Many thanks for your help.

[George Ford]

Basis DID is:

y = b0 + b1*post + b2*treated + d*post*treated

post is the treatment period == 1
treated is the group that is treated, which == 1 for all period if the group is treated (0 otherwise)
post*treated is = 1 for the treated group during the treatment period

I think, in this data,

date == post
Treatment == post*treated

To keep the dicta proper,

g post = Date
egen treated = max(Treatment), by(Cafe)
reg Quantitybeef post treated c.post#c.treated