sub select not work

[appxq]

SELECT aname, ( SELECT first pname as pname FROM zdata_prov WHERE pcode="10" ) AS ppp FROM zdata_amphur

result=>

[{_id: "67c3d655e88285a3d0839786", aname: "เขตพระนคร", ppp: null},…]
0
:
{_id: "67c3d655e88285a3d0839786", aname: "เขตพระนคร", ppp: null}
1
:
{_id: "67c3d655e88285a3d0839787", aname: "เขตดุสิต", ppp: null}

Why is that?

[appxq]

SELECT (SELECT * FROM zdata_amphur) as aname FROM zdata_prov

result=> null. Why is that?