Q: Hi, previously I had placed all my songs in my external drive instead of in my macbook so that the songs in iTunes can only play when i plugged in my hard disk. Now, I got a new macbook so I was wondering how to transfer that library

I think this is the article you are looking for...  How to move your iTunes library to a new computer - Apple Support

I don't understand.  Consolidating libraries was not part of the instructions in the link I provided.  Why were you consolidating (I assume iTunes > Library > Organize )?  You don't have to if you copied the old itunes folder to music on the new computer.  No consolidation necessary.  Did you get an error or something?

Moving a library: Quick answer if you use iTunes' default preferences settings:  Copy the entire iTunes folder (and in doing so all its sub-folders and files) intact to the other drive.  Hold down the option (alt) key (shift on Windows) and open iTunes.  At the select prompt choose the iTunes Library.itl file in the copied iTunes folder.

When this is to a new computer put the copied iTunes folder in the default location of Macintosh HD > Users > *User Name* > Music  then you don't even need to start with the option key held down, iTunes will automatically look for it there.  (Make sure there isn't anything already in the iTunes folder there that you want to keep since you will be replacing it with the one you are moving.)  Also remember to authorize the computer in iTunes to your Apple ID if you use this to sync to Apple mobile devices.

See Make a split library portable.

tt2

I do not think the OP wants to make the library portable.

my mac does not have enough memory to consolidate.

I suspect the library needs to be in a portable shape to move smoothly from one machine to another. There is likely not enough room to consolidate the library to the standard folder on the internal drive or the library, or more likely media, wouldn't have been placed on an external drive. Without knowing the size of the library or the drives involved it isn't clear if the endpoint of having the library all on the new computer is achievable, but transforming into a portable shape is should help either way.

tt2

From various posts I think your ultimate goal is not clear to us.  I think, however, what you need to do is what I instructed earlier.  First transfer your current library on your old computer to the new one. This will continue to use your media on the external drive as before, so there should be no space issues unless the drive on the new computer is smaller than the drive on the old one (quite possible with new computers, in which case you need to tell us).  If you want it all on the internal drive of the new computer, and there is room, you can then consolidate so everything will be on the internal drive of the new computer.