(select concat(0x3a,char(64),char(52),char(51),char(55),char(48),char(49),user(),char(64),char(49),char(48),char(55),char(51),char(52)))

Here’s what the expression does and what it would produce in MySQL:

• 0x3a is the ASCII for colon ":".
• char(64) is "@"
• char(52), char(51), char(55), char(48), char(49) are the digits 4, 3, 7, 0, 1, so that sequence builds "43701".
• user() returns the current MySQL user (in MySQL this is typically something like user@host, e.g., root@localhost).
• The whole concat(...) builds a single string: ":" + "@" + "43701" + USER() + "@" + "10734"

So the final string is: :@43701<USER()>@10734

Example: if USER() is root@localhost, you’d get: :@43701root@localhost@10734

Note: This pattern looks like a small payload that could be used in an injection test to leak the current user. If you’re studying SQL injection, also review safe coding practices (prepared statements, parameterized queries, input validation, least privilege). If you want, I can help explain how to defend against such patterns or show safe, non-exploitable examples.