Can we put or in 2 regex conditions?
If no, is there any alternative?
index = idx1 | regex name = ^Aa or id = ^101
If I follow your question it should just be a matter of crafting your expression properly
index = idx1 | regex name="\w|\d"
Should return results where the value of the field called name is a word or digit character
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Can we use upper function also to make the regular expression search case insensitive or is there any other way ?
Yes, you should be able to use any valid PCRE.
Splunk's documentation can explain this much better than I: