Issue with query.exec_ in PyQt5

[fifth]

query = QtSql.QSqlQuery(db)

query.exec_("SELECT * FROM userscredentials")

print(query.value(0))

As above, your query is not pointing at a valid record. You don't call query.next() (or first as d_stranz said). If your expecting a single record you can do;

if query.next():
    print(query.value(0))

if query.next():
    print(query.value(0))

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or for more results use a while loop:

while query.next():
    print(query.value(0))

while query.next():
    print(query.value(0))

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