SQL question

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Here's a question for the SQL guru's out there, which I've been trying to
solve for the last couple of hours. There's got to be a solution to this, but
somehow I can't find it.

Tables:

table1 (
uid int PK,
uname varchar(64)
)

table2 (
uid int FK to table1,
xuid int FK to table 1
)

table3 (
uid int FK to table1,
yuid int FK to table1
)

There might be more tables of the type like table2 and table3, but I'd already
be happy to solve the puzzle with the 3 tables above.
Ok, assume table1 is the master table - in my case a table used for login
authentication (some columns removed above)
table2 and table3 are tables where the uid always references to the uid in
table1. The second "uid" (xuid and yuid in this example) references to
another uid record in table1. The problem is that there may or may not be
entries in table2 (or table3) referencing a specific uid in their second uid
field.
Maybe some data:

table1:
1 test1
2 test2
3 test3

table2:
1 2
1 3
3 1

table3:
1 2
2 3
3 2

What I want to do in a view is the following resultset:

uid uname xuid yuid
1 test1 2 2
1 test1 3
2 test2 3
3 test3 1
3 test3 2

So basically I want to know which uid is connected to which uid, one
relationship per row. So xuid and yuid shall be identical if records exist in
both table2 and table3 or the value shall be NULL if a corresponding record
can't be found in either table2 or table3.

Can anyone here help me out?

Thanks a lot

UC

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