SQL Server TRIGGER IF值存在，然后将其更改为其他

Question

I have a table called dbo.PBXDATA . I want to set a trigger where if the value of column SALES_REP equals a specific value(int), then change that value to the name of the sales_rep in the Table column. Below is what I have so far. Any hints would be great. Thank you.

CREATE TRIGGER dbo.PBXDATA_trgIUD_sales_rep
   ON  dbo.PBXDATA
   AFTER INSERT,UPDATE
AS 
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;
SELECT CAST(WHEN SALES_REP = '101'
THEN 'Ryan Kosterow'
ELSE 'NULL'
END as NVARCHAR) FROM dbo.PBXDATA

SELECT CAST(WHEN SALES_REP = '115'
THEN 'Robert Messing'
ELSE 'NULL'
END as NVARCHAR) FROM dbo.PBXDATA

SELECT CAST(WHEN SALES_REP = '114'
THEN 'Paul Clark'
ELSE 'NULL'
END as NVARCHAR) FROM dbo.PBXDATA

SELECT CAST(WHEN SALES_REP = '110'
THEN 'Aaron Townsley'
ELSE 'NULL'
END as NVARCHAR) FROM dbo.PBXDATA

END
GO

Answer 1

I think you meant to perform a UPDATE operation rather SELECT . Again, you are actually trying to use CASE expression and your current syntax CAST(WHEN SALES_REP = '101' ... is wrong. You can try like below:

UPDATE dbo.PBXDATA SET SALES_REP = CASE WHEN SALES_REP = '101' THEN 'Ryan Kosterow'
WHEN SALES_REP = '115' THEN 'Robert Messing' 
WHEN SALES_REP = '114' THEN 'Paul Clark'
WHEN SALES_REP = '110' THEN 'Aaron Townsley'
ELSE 'NULL' END

Answer 2

You can use the special inserted table to perform your updates. This table will be available in the trigger and will contain the row being updated. This could be the code:

update inserted 
set SALES_REP = 'Ryan Kosterow'
where SALES_REP = '101'

update inserted 
set SALES_REP = 'Robert Messing'
where SALES_REP = '115'

update inserted 
set SALES_REP = 'Paul Clerk'
where SALES_REP = '114'

update inserted 
set SALES_REP = 'Aaron Townsley'
where SALES_REP = '110'

Answer 3

This is a bad design. You really should have a SALES_REP_NAMES table which you could JOIN to the PBXDATA table when you need to have a query that outputs names. It would look like

SALES_REP_ID    NAME
------------    ----------------
110             Aaron Townsley
etc...

Than you could do something like:

SELECT
  *
FROM
  PBXDATA P
  JOIN SALES_REP_NAMES N
    ON P.SALES_REP = N.SALES_REP_ID

However IF you really WANT to do it via a TRIGGER it should look like the following. Note that it avoids recursive nesting BY checking IF the TRIGGER needs to do an UPDATE.

CREATE TRIGGER dbo.PBXDATA_trgIUD_sales_rep ON dbo.PBXDATA
  AFTER INSERT, UPDATE
AS
  BEGIN
    SET NOCOUNT ON;
    IF UPDATE(SALES_REP) 
      UPDATE
        p
      SET
        p.SALES_REP = CASE WHEN SALES_REP = '101' THEN 'Ryan Kosterow'
                         WHEN SALES_REP = '115' THEN 'Robert Messing'
                         WHEN SALES_REP = '114' THEN 'Paul Clark'
                         WHEN SALES_REP = '110' THEN 'Aaron Townsley'
                    END
      FROM
        INSERTED I
        JOIN PBXDATA P
          ON I.SALES_REP = P.SALES_REP
      WHERE
        I.SALES_REP IN ( '101', '115', '114', '110' )

  END 
GO