将计算列插入 table

Question

我一直在尝试在 SQL 中做一些事情，但我无法在 Stack Overflow 上找到正确的答案。我已经创建了一个 table（称为 RMBS_STANDARDIZED），它有一列 LOAN_PERC_ISSUER。 table 是我标准化命名约定的其他几个 table 的联合。

加载 table 后我想做的是用这个内部查询更新它（注意当我运行这个它 returns 返回正确的值但显然单列）。因此，我想将返回的查询存储在 table.

SELECT 
    ISSUER_SERIES,
    SUM(COALESCE(LOAN_BALANCE, 0)) AS TOTAL_BALANCE 
FROM 
    RMBS_STANDARDIZED 
GROUP BY 
    ISSUER_SERIES

我尝试使用的插入查询是

INSERT INTO RMBS_STANDARDIZED (LOAN_PERC_ISSUER)
    SELECT
        COALESCE(T1.LOAN_BALANCE, 0) / T2.TOTAL_BALANCE
    FROM 
        RMBS_STANDARDIZED T1
    LEFT JOIN
        (SELECT 
             ISSUER_SERIES,
             SUM(COALESCE(LOAN_BALANCE, 0)) AS TOTAL_BALANCE 
         FROM 
             RMBS_STANDARDIZED 
         GROUP BY 
             ISSUER_SERIES) T2 ON T1.ISSUER_SERIES = T2.ISSUER_SERIES

但是我得到以下错误

Cannot insert the value NULL into column 'ISSUER'

如果我调整 ISSUER 列以允许 NULL，则该列不会更新或保持为 NULL。

或者，我尝试了以下方法

ALTER TABLE RMBS_STANDARDIZED  
    ADD New_Column AS (SELECT
                           COALESCE(T1.LOAN_BALANCE, 0) /  T2.TOTAL_BALANCE
                       FROM 
                           RMBS_STANDARDIZED T1
                       LEFT JOIN
                           (SELECT 
                                ISSUER_SERIES,
                                SUM(COALESCE(LOAN_BALANCE, 0)) AS TOTAL_BALANCE 
                            FROM 
                                RMBS_STANDARDIZED GROUP BY ISSUER_SERIES) T2
                           ON T1.ISSUER_SERIES = T2.ISSUER_SERIES)

但是得到如下错误

Subqueries are not allowed in this context. Only scalar expressions are allowed.

任何想法都会有所帮助。在创建最终 table 之前，我最好使用 CTE 或创建 temp/hash table？我正在使用 SQL 服务器和 SQL 服务器管理工作室。

Answer 1

您的第一个查询失败，因为 LOAN_PERC_ISSUER 有一个 NOT NULL 约束。将您的查询重写为：

SELECT COALESCE(T1.LOAN_BALANCE / T2.TOTAL_BALANCE, 0)
FROM   RMBS_STANDARDIZED AS T1
       LEFT OUTER JOIN (SELECT ISSUER_SERIES, 
                               SUM(COALESCE(LOAN_BALANCE, 0)) AS TOTAL_BALANCE
                        FROM   RMBS_STANDARDIZED
                        GROUP  BY ISSUER_SERIES) AS T2 
           ON T1.ISSUER_SERIES = T2.ISSUER_SERIES;

计算列不能有任何类型的子查询，并且必须仅使用来自行值的数据。有可能将查询放入 UDF 并将 UDF 用于计算列，但不太推荐...

一个更合适的方法是使用触发器

将计算列插入 table

Insert calculated column into a table

sql-server

inner-join

alter

sql-insert