I have a page which looks like this:
╔═══╦════════╦══════╦═══╗
║ A ║ B ║ C ║ D ║
╠═══╬════════╬══════╬═══╣
║ 1 ║ User A ║ 144 ║ ║
║ 2 ║ User B ║ 5478 ║ ║
║ 3 ║ User A ║ 2156 ║ ║
╚═══╩════════╩══════╩═══╝
I'd like to populate column D with data from another page:
╔═════╦══════╦═══╦════════╗
║ A ║ B ║ C ║ D ║
╠═════╬══════╬═══╬════════╣
║ ABC ║ User ║ B ║ User B ║
║ DEF ║ User ║ A ║ User A ║
╚═════╩══════╩═══╩════════╝
Note: column D is a concatenation of column B and C.
In this case, it should populate column D on page 1 with the data from column A on page 2 matching Page1!B to Page2!D, which should produce the following combined table:
╔═══╦════════╦══════╦═════╗
║ A ║ B ║ C ║ D ║
╠═══╬════════╬══════╬═════╣
║ 1 ║ User A ║ 144 ║ DEF ║
║ 2 ║ User B ║ 5478 ║ ABC ║
║ 3 ║ User A ║ 2156 ║ DEF ║
╚═══╩════════╩══════╩═════╝
How can I do this in Google Spreadsheets?