I know how to write simpel code of a macro to complete one task:
e.g. drop obervations whose var1 value is missing.

global drop_missing "drop if var1 =."

But how can I write simpel code of a macro to complete multiple tasks?
e.g. drop obervations whose var1 value is missing, then drop those whose var2 value is missing, then drop those whose var3 value is missing.

global drop_missing "drop if var1 =. drop if var2 =. drop if var3 =."

The above line of code is definitively wrong. How can I write this code?

I do not know how to properly phrase this question, so I cannot search and find any previous Q&As.

Thank you for any advice/comments!