update statement not executing

问题

I am trying to write an UPDATE query that can check for a null value in one of the fields. I have three conditions, two are mandatory, of three fields. itemCode and itemCheckDigit will always exist, itemSuffix is possibily Null.

There may be multiple records where itemCode and itemCheckDigit together are equal to other records, itemSuffix is the unquie identifier, only one instance will exist though where itemSuffix is Null and it will never be duplicated.

UPDATE item
SET          itemImageFileName = ''' + @fileName + '''
WHERE        (itemCode = ''' + @itemCode5 + ''') AND (itemCheckDigit = ''' + @itemCkDigit + ''') AND (itemSuffix IS NULL);

This is what I think I would like to do, but it is not working.

回答1:

Your problem is that you are wrapping tick marks around your parameters in your statement so when it's evaluated it looking for stuff from the item table where itemCode is 'toy' (note the single quotes)

The string concatenation you are doing is how one would, poorly, add parameters to their dynamic queries. Instead, take the tick marks out like so

UPDATE
    item
SET
    itemImageFileName = @fileName
WHERE
    (itemCode = @itemCode5 ) 
    AND (itemCheckDigit = @itemCkDigit) 
    AND (itemSuffix IS NULL);

To handle optional search parameters, this article by Bill Graziano is excellent: Using Dynamic SQL in Stored Procedures. I find that is strikes a good balance between avoiding the query recompilations of setting the recompile option on and avoiding table scans.

Please to enjoy this code. It create a temporary table to simulate your actual item table and loads it up with 8 rows of data. I declare some parameters which you most likely wont' need to do as the ado.net library will do some of that magic for you.

Based on the values supplied for the first 3 parameters, you will get an equivalent match to a row in the table and will update the filename value. In my example, you will see the all NULL row will have the filename changed from f07.bar to f07.bar.updated.

The print statement is not required but I put it in there so that you can see the query that is built as an aid in understanding the pattern.

IF NOT EXISTS (SELECT * FROM tempdb.sys.tables T WHERE T.name like '%#item%')
BEGIN
    CREATE TABLE 
        #item
    (
        itemid int identity(1,1) NOT NULL PRIMARY KEY
    ,   itemCode varchar(10) NULL
    ,   itemCheckDigit varchar(10) NULL
    ,   itemSuffx varchar(10) NULL
    ,   itemImageFileName varchar(50) 
    )
    INSERT INTO
        #item
    -- 2008+
    --table value constructor (VALUES allows for anonymous table declaration) {2008}
    --http://technet.microsoft.com/en-us/library/dd776382.aspx
    VALUES 
        ('abc', 'X', 'cba', 'f00.bar')
    ,   ('ac', NULL, 'ca', 'f01.bar')
    ,   ('ab', 'x', NULL, 'f02.bar')
    ,   ('a', NULL, NULL, 'f03.bar')

    ,   (NULL, 'X', 'cba', 'f04.bar')
    ,   (NULL, NULL, 'ca', 'f05.bar')
    ,   (NULL, 'x', NULL, 'f06.bar')
    ,   (NULL, NULL, NULL, 'f07.bar')
END

SELECT * 
FROM #item I;

-- These correspond to your parameters
DECLARE
    @itemCode5 varchar(10)
,   @itemCkDigit varchar(10)
,   @itemSuffx varchar(10)
,   @fileName varchar(50)

-- Using the above table, populate these as
-- you see fit to verify it's behaving as expected
-- This example is for all NULLs 
SELECT
    @itemCode5 = NULL
,   @itemCkDigit = NULL
,   @itemSuffx = NULL
,   @fileName = 'f07.bar.updated'


DECLARE
    @query nvarchar(max)

SET
    @query = N'
UPDATE
    I
SET
    itemImageFileName = @fileName
FROM
    #item I
WHERE
    1=1
' ;


IF @itemCode5 IS NOT NULL
BEGIN
    SET @query += '    AND I.itemCode = @itemCode5 ' + char(13)
END
ELSE
BEGIN
    -- These else clauses may not be neccessary depending on 
    -- what your data looks like and your intentions
    SET @query += '    AND I.itemCode IS NULL ' + char(13)
END

IF @itemCkDigit IS NOT NULL 
BEGIN
    SET @query += '    AND I.itemCheckDigit = @itemCkDigit ' + char(13)
END
ELSE
BEGIN
    SET @query += '    AND I.itemCheckDigit IS NULL ' + char(13)
END

IF @itemSuffx IS NOT NULL 
BEGIN
    SET @query += '    AND I.itemSuffx = @itemSuffx ' + char(13)
END
ELSE
BEGIN
    SET @query += '    AND I.itemSuffx IS NULL ' + char(13)
END

PRINT @query

EXECUTE sp_executeSQL @query   
,   N'@itemCode5 varchar(10), @itemCkDigit varchar(10), @itemSuffx varchar(10), @fileName varchar(50)'
,   @itemCode5 = @itemCode5
,   @itemCkDigit = @itemCkDigit
,   @itemSuffx = @itemSuffx
,   @fileName = @fileName;

-- observe that all null row is now displaying
-- f07.bar.updated instead of f07.bar
SELECT * 
FROM #item I;

Before

itemid  itemCode   itemCheckDigit   itemSuffx    itemImageFileName
1       abc        X                cba          f00.bar
2       ac         NULL             ca           f01.bar
3       ab         x                NULL         f02.bar
4       a          NULL             NULL         f03.bar
5       NULL       X                cba          f04.bar
6       NULL       NULL             ca           f05.bar
7       NULL       x                NULL         f06.bar
8       NULL       NULL             NULL         f07.bar

after

itemid  itemCode   itemCheckDigit   itemSuffx    itemImageFileName
1       abc        X                cba          f00.bar
2       ac         NULL             ca           f01.bar
3       ab         x                NULL         f02.bar
4       a          NULL             NULL         f03.bar
5       NULL       X                cba          f04.bar
6       NULL       NULL             ca           f05.bar
7       NULL       x                NULL         f06.bar
8       NULL       NULL             NULL         f07.bar.updated

来源：https://stackoverflow.com/questions/7621364/update-statement-not-executing

标签

sql

tsql

sql-server-express

sql-update