SQL:根据大小写表达式添加一个新列,并从另一个表中查找值

分两步进行:

ALTER TABLE Portfolio.Trades ADD Multiplier decimal(7,3);

UPDATE T
    SET Multiplier = (CASE WHEN T.Type = 'Equity' Then 1
                           WHEN T.Type = 'Corp' Then 0.1
                           WHEN T.Type = 'Option' Then 100
                           ELSE (SELECT CS.ContractSize
                                 FROM Portfolio.ContractSize CS
                                 WHERE T.Identifier = CS.ContractSize)
                       END)
    FROM Portfolio.Trades T;

我猜 ON

UPDATE T
    SET Multiplier = (CASE WHEN T.Type = 'Equity' Then 1
                           WHEN T.Type = 'Corp' Then 0.1
                           WHEN T.Type = 'Option' Then 100
                           ELSE T.Identifier)
                       END)
    FROM Portfolio.Trades T;

为什么要在表中添加列?也可以创建视图。

CREATE VIEW myView AS
    SELECT *, -- your real column list here
        CAST(CASE
         WHEN Type = 'Equity' Then 1
         WHEN Type = 'Corp' Then 0.1
         WHEN Type = 'Option' Then 100
         ELSE
           (SELECT ContractSize 
            FROM Portfolio.ContractSize CS
            WHERE T.Identifier = CS.ContractSize)
         END AS decimal(7,3)) AS  Multiplier
    FROM
    Portfolio.Trades T;

ALTER TABLE Portfolio.Trades
ADD Multiplier decimal(7,3) AS
(
CASE 
 WHEN Type = 'Equity' Then 1
 WHEN Type = 'Corp' Then 0.1
 WHEN Type = 'Option' Then 100
ELSE
 (SELECT ContractSize FROM Portfolio.ContractSize CS
 JOIN Portfolio.Trades T
 ON T.Identifier = CS.ContractSize)END
)