How to change upper case to lower via search/replace?

This posts explain how the emacs in-built query-replace-regexp command can be used to convert upper-cased strings to lower case.

• Do M-x query-replace-regexp or use the default binding C-M-% to activate the regular expression search/replace.
• Enter the regexp for the strings to be replaced in the *Query regexp:" field. For instance, if I want to convert I_data and Q_data to i_data and q_data respectively, then my search regular expression will be \([IQ]\)_data.
• It is important to use the escaped grouping brackets \( and \) to wrap an expression that you want to upcase or downcase.
• In the next Query replace: prompt, the expression will be \,(downcase \1)_data¹.