如何解决错误:运算符不唯一:动态SQL查询中的“未知”-“未知”?

我在存储过程中有一个执行块,我正在动态执行查询:

execute 'create table raw_mine.financial_multicase_xwalk_' || target_date || '
as
select distinct
  a.cvr_mnth_dt
, a.filler_string_10
, a.alt_prsn_id
, a.member_id
from raw_mine.rstag_mine_TO_CGT_MBRSHP_' || target_date || ' a
left join
raw_mine.rstag_mine_TO_CGT_FIN_' || target_date || ' b
on a.filler_string_10 = b.filler_string_10
and a.member_id = b.member_id
and left ( a.cvr_mnth_dt, 6) = left ( b.cvr_mnth_dt, 6)
left join
raw_mine.rstag_mine_TO_CGT_FIN_' || target_date || ' cp
on a.filler_string_10 = cp.filler_string_10
and a.alt_prsn_id = cp.alt_prsn_id
and left ( a.cvr_mnth_dt, 6) = left ( cp.cvr_mnth_dt, 6)
left join
raw_mine.member_xwalk_dulality_' || target_date || ' c
on a.alt_prsn_id = c.alt_prsn_id
and left ( a.cvr_mnth_dt, 6) = left ( replace ( c.cvr_mnth_dt, '-', ''), 6)
where nullif ( c.alt_prsn_id, '') is null
and cp.alt_prsn_id is not null
and cp.member_id != a.member_id;';

所有列都是varchars和 target_date 是过程的输入参数,我得到一个错误

SQL错误[42725]:错误:运算符不唯一:“未知”-“未知”

提示:无法选择最佳候选运算符。您可能需要添加显式类型强制转换。

知道怎么解决这个问题吗?

此查询在过程外部执行时有效。