Defensive Database Programming - Red Gate Software

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Chapter 6: Common Problems with Data IntegrityNewBarcodeEND ;)SELECT d.ItemLabel ,CURRENT_TIMESTAMP ,d.Barcode ,i.BarcodeFROM inserted AS iINNER JOIN deleted AS dON i.ItemLabel = d.ItemLabelWHERE ( ( d.Barcode i.Barcode )OR ( d.Barcode IS NULLAND i.Barcode IS NOT NULL)OR ( d.Barcode IS NOT NULLAND i.Barcode IS NULL)) ;Listing 6-52: Altering our trigger so that is does not allow modification of theprimary key column.To test this trigger, we can rerun Listings 6-48 and 6-51. If, however, our business rulesallow changes to be made to labels on items, then we need some other immutablecolumn; some column that cannot be changed, and so can uniquely identify a row.This is one of those cases when IDENTITY columns are so useful. Listing 6-53 adds anIDENTITY column and creates a UNIQUE constraint to make sure that the IDENTITYcolumn is always unique.ALTER TABLE dbo.ItemsADD ItemID int NOT NULLIDENTITY(1, 1) ;GO202
Chapter 6: Common Problems with Data IntegrityALTER TABLE dbo.ItemsADD CONSTRAINT UNQ_Items_ItemID#UNIQUE ( ItemID ) ;Listing 6-53: Creating an IDENTITY column that holds only unique values.This new IDENTITY column, ItemID, is immutable; it is not possible to modify anIDENTITY column, as Listing 6-54 demonstrates.UPDATE dbo.ItemsSET ItemID = -1WHERE ItemID = 1 ;Msg 8102, Level 16, State 1, Line 1Cannot update identity column 'ItemID'.Listing 6-54: It is not possible to modify IDENTITY columns.We can now use our immutable ItemId column so that it does not have to assume thatthe primary key will never change, and so fixes the weakness in our trigger, as shown inListing 6-55.ALTER TRIGGER dbo.Items_LogBarcodeChange ON dbo.ItemsFOR UPDATEASBEGIN ;INSERT INTO dbo.ItemBarcodeChangeLog( ItemLabel ,ModificationDateTime ,OldBarcode ,NewBarcode)SELECT i.ItemLabel ,CURRENT_TIMESTAMP,d.Barcode ,i.Barcode203
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Chapter 2: Code Vulnerabilities due
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Enforcing Data Integrity in the App
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About the AuthorAlex Kuznetsov has
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IntroductionResilient T-SQL code is
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IntroductionCh. 02: Code Vulnerabil
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IntroductionSpecific examples demon
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IntroductionWhat this book does not
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Chapter 1: Basic Defensive Database
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Chapter 2: Code Vulnerabilitiesdue
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Chapter 3: Surviving Changes to Dat
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Chapter 4: When Upgrading Breaks Co
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Chapter 5: Reusing T-SQL CodeThe Da
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Chapter 5: Reusing T-SQL CodeIt is
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Chapter 5: Reusing T-SQL CodeAverag
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Chapter 5: Reusing T-SQL CodeBEGINS
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Chapter 5: Reusing T-SQL CodeWe als
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Chapter 5: Reusing T-SQL CodeLet's
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Chapter 5: Reusing T-SQL CodeStateC
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Chapter 5: Reusing T-SQL CodeStateC
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Chapter 5: Reusing T-SQL CodeBEGIN
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Chapter 5: Reusing T-SQL CodeSELECT
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Chapter 7: Advanced Use of Constrai
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Chapter 8: Defensive ErrorHandlingT
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Chapter 8: Defensive Error Handling
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Defensive Database Programming - Red Gate Software

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