to_date的转换表示缺少右括号

很多事情。

SQL> with test (year, month) as
  2    (select '2022', '4' from dual)
  3  select to_date(year ||'-'|| lpad(month, 2, '0') || '-01', 'yyyy-mm-dd') result
  4  from test;

RESULT
--------------------
01-APR-22

SQL>

不过,由于你似乎想要当月的1号,你可以将其缩短为

SQL> with test (year, month) as
  2    (select '2022', '4' from dual)
  3  select to_date(year || month, 'yyyymm') result
  4  from test;

RESULT
--------------------
01-APR-22

SQL>

这个 LAST_DAY 选项:

SQL> with test (year, month) as
  2    (select '2022', '4' from dual)
  3  select
  4             to_date(year  ||'-'||  lpad(month,2,0)  ||'-01','YYYY-MM-DD')  as firstday,
  5    last_day(to_date(year  ||'-'||  lpad(month,2,0)  ||'-01','YYYY-MM-DD')) as lastday
  6  from test;

FIRSTDAY   LASTDAY
---------- ----------
01.04.2022 30.04.2022

SQL>