How to modify the built-in 'fetch' function so that it can select columns flexibly?

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Simon
Simon 2022-11-9
评论： Simon 2022-11-10
I was trying to write a function which fetch only the columns I like from a MySQL table.
easy_fetch(conn, 'mytable', 'A', 'B') % error, incorrect sqlquery string
easy_fecth(conn, 'mytable', 'A,', 'B') % this works but clumsy
function T = easy_fetch (conn, tablename, varargin)
sqlquery = ['select ' varargin{:} ' from ' tablename]; % I don't know how to insert commas here.
T = fetch(conn, sqlquery);
end
That fuction does not create right sql query string because it doesn't have commas between A and B
wrong_string = 'select A B from mytable'.
fetch(conn, wrong_string) % error
% the correct query string should have commas between A and B
right_string = 'select A, B from mytable'
fecth(conn, right_string) % success
How would I put ',' between A and B in the easy_fetch function? Or is there better way to flexibly fetch columns? I have checked out a couple packages shared in File Exchange. None has codes I can use. Thanks for any suggestions.

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采纳的回答

Steven Lord
Steven Lord 2022-11-10
Ran in:
s = {'Larry', 'Curly', 'and Moe'}
s = 1×3 cell array
{'Larry'} {'Curly'} {'and Moe'}
s2 = strjoin(s, ', ')
s2 = 'Larry, Curly, and Moe'
  1 个评论
Simon
Simon 2022-11-10
I am very thankful for your solution. It works! The modified version does what I want.
T = easy_fetch(conn, 'mytable', 'A', 'B') % works smoothly :-)
%%
function T = easy_fetch (conn, tablename, varargin)
cols = strjoin(varargin, ',');
sqlquery = ['select ' cols ' from ' tablename];
T = fetch(conn, sqlquery);
end

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