如何对货币ID配对表去重？SQL语句优化求助

修改后的SQL语句如下：

with 
    cte_currencies as (
        select 'GBP' as CurrencyId union select 'USD' union select 'DKK' union select 'GBX'
    ), cte_combined_crossings as (
        select b.CurrencyId as baseCurrencyId, q.CurrencyId as QuoteCurrencyId 
        from cte_currencies b cross join cte_currencies q 
        where b.CurrencyId < q.CurrencyId
    )

select * from cte_combined_crossings

实现思路 #

把原SQL的过滤条件从not b.CurrencyId=q.CurrencyId替换成b.CurrencyId < q.CurrencyId，通过字典序比较货币ID，只保留基准货币ID字典序小于报价货币ID的配对，自动剔除DKK/GBP与GBP/DKK这类双向重复的条目，输出结果完全匹配目标表需求。

内容的提问来源于stack exchange，提问作者Liam