COLUMNS_UPDATED (Transact-SQL)

आलेख
12/29/2022

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

This function returns a varbinary bit pattern indicating the inserted or updated columns of a table or view. Use COLUMNS_UPDATED anywhere inside the body of a Transact-SQL INSERT or UPDATE trigger to test whether the trigger should execute certain actions.

Transact-SQL syntax conventions

Syntax

COLUMNS_UPDATED ( )

Return types

varbinary

Remarks

COLUMNS_UPDATED tests for UPDATE or INSERT actions performed on multiple columns. To test for UPDATE or INSERT attempts on one column, use UPDATE().

COLUMNS_UPDATED returns one or more bytes that are ordered from left to right. The rightmost bit of each byte is the least significant bit. The rightmost bit of the leftmost byte represents the first table column in the table, the next bit to the left represents the second column, and so on. COLUMNS_UPDATED returns multiple bytes if the table on which the trigger is created contains more than eight columns, with the least significant byte being the leftmost. COLUMNS_UPDATED returns TRUE for all columns in INSERT actions because the columns have either explicit values or implicit (NULL) values inserted.

To test for updates or inserts to specific columns, follow the syntax with a bitwise operator and an integer bitmask of the tested columns. For example, say that table t1 contains columns C1, C2, C3, C4, and C5. To verify that columns C2, C3, and C4 all successfully updated (with table t1 having an UPDATE trigger), follow the syntax with & 14. To test whether only column C2 is updated, specify & 2. See Example A and Example B for actual examples.

Use COLUMNS_UPDATED anywhere inside a Transact-SQL INSERT or UPDATE trigger.

The ORDINAL_POSITION column of the INFORMATION_SCHEMA.COLUMNS view is not compatible with the bit pattern of columns returned by COLUMNS_UPDATED. To obtain a bit pattern compatible with COLUMNS_UPDATED, reference the ColumnID property of the COLUMNPROPERTY system function when querying the INFORMATION_SCHEMA.COLUMNS view, as shown in the following example.

SELECT TABLE_NAME, COLUMN_NAME,  
    COLUMNPROPERTY(OBJECT_ID(TABLE_SCHEMA + '.' + TABLE_NAME),  
    COLUMN_NAME, 'ColumnID') AS COLUMN_ID  
FROM AdventureWorks2022.INFORMATION_SCHEMA.COLUMNS  
WHERE TABLE_NAME = 'Person';

If a trigger applies to a column, the COLUMNS_UPDATED returns as true or 1, even if the column value remains unchanged. This is by-design, and the trigger should implement business logic that determines if the insert/update/delete operation is permissible or not.

Column sets

When a column set is defined on a table, the COLUMNS_UPDATED function behaves in the following ways:

When explicitly updating a member column of the column set, the corresponding bit for that column is set to 1, and the column set bit is set to 1.
When a explicitly updating a column set, the column set bit is set to 1, and the bits for all of the sparse columns in that table are set to 1.
For insert operations, all bits are set to 1.

Because changes to a column set cause the bits of all columns in the column set to reset to 1, unchanged columns in a column set will appear modified. See Use Column Sets for more information about column sets.

Examples

A. Using COLUMNS_UPDATED to test the first eight columns of a table

This example creates two tables: employeeData and auditEmployeeData. The employeeData table holds sensitive employee payroll information and human resources department members can modify it. If the social security number (SSN), yearly salary, or bank account number for an employee changes, an audit record is generated and inserted into the auditEmployeeData audit table.

With the COLUMNS_UPDATED() function, we can quickly test for any changes made to columns containing sensitive employee information. Using COLUMNS_UPDATED() this way works only when trying to detect changes to the first eight columns in the table.

USE AdventureWorks2022;  
GO  
IF EXISTS(SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES  
   WHERE TABLE_NAME = 'employeeData')  
   DROP TABLE employeeData;  
IF EXISTS(SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES  
   WHERE TABLE_NAME = 'auditEmployeeData')  
   DROP TABLE auditEmployeeData;  
GO  
CREATE TABLE dbo.employeeData (  
   emp_id INT NOT NULL PRIMARY KEY,  
   emp_bankAccountNumber CHAR (10) NOT NULL,  
   emp_salary INT NOT NULL,  
   emp_SSN CHAR (11) NOT NULL,  
   emp_lname NCHAR (32) NOT NULL,  
   emp_fname NCHAR (32) NOT NULL,  
   emp_manager INT NOT NULL  
   );  
GO  
CREATE TABLE dbo.auditEmployeeData (  
   audit_log_id uniqueidentifier DEFAULT NEWID() PRIMARY KEY,  
   audit_log_type CHAR (3) NOT NULL,  
   audit_emp_id INT NOT NULL,  
   audit_emp_bankAccountNumber CHAR (10) NULL,  
   audit_emp_salary INT NULL,  
   audit_emp_SSN CHAR (11) NULL,  
   audit_user sysname DEFAULT SUSER_SNAME(),  
   audit_changed DATETIME DEFAULT GETDATE()  
   );  
GO  
CREATE TRIGGER dbo.updEmployeeData   
ON dbo.employeeData   
AFTER UPDATE AS  
/* Check whether columns 2, 3 or 4 have been updated. If any or all  
columns 2, 3 or 4 have been changed, create an audit record.
The bitmask is: power(2, (2-1)) + power(2, (3-1)) + power(2, (4-1)) = 14.
This bitmask translates into base_10 as: 2 + 4 + 8 = 14.
To test whether all columns 2, 3, and 4 are updated, use = 14 instead of > 0  
(below). */
  
   IF (COLUMNS_UPDATED() & 14) > 0  
/* Use IF (COLUMNS_UPDATED() & 14) = 14 to see whether all columns 2, 3,   
and 4 are updated. */  
      BEGIN  
-- Audit OLD record.  
      INSERT INTO dbo.auditEmployeeData  
         (audit_log_type,  
         audit_emp_id,  
         audit_emp_bankAccountNumber,  
         audit_emp_salary,  
         audit_emp_SSN)  
         SELECT 'OLD',   
            del.emp_id,  
            del.emp_bankAccountNumber,  
            del.emp_salary,  
            del.emp_SSN  
         FROM deleted del;  
  
-- Audit NEW record.  
      INSERT INTO dbo.auditEmployeeData  
         (audit_log_type,  
         audit_emp_id,  
         audit_emp_bankAccountNumber,  
         audit_emp_salary,  
         audit_emp_SSN)  
         SELECT 'NEW',  
            ins.emp_id,  
            ins.emp_bankAccountNumber,  
            ins.emp_salary,  
            ins.emp_SSN  
         FROM inserted ins;  
   END;  
GO  
  
/* Inserting a new employee does not cause the UPDATE trigger to fire. */  
INSERT INTO employeeData  
   VALUES ( 101, 'USA-987-01', 23000, 'R-M53550M', N'Mendel', N'Roland', 32);  
GO  
  
/* Updating the employee record for employee number 101 to change the   
salary to 51000 causes the UPDATE trigger to fire and an audit trail to   
be produced. */  
  
UPDATE dbo.employeeData  
   SET emp_salary = 51000  
   WHERE emp_id = 101;  
GO  
SELECT * FROM auditEmployeeData;  
GO  
  
/* Updating the employee record for employee number 101 to change both   
the bank account number and social security number (SSN) causes the   
UPDATE trigger to fire and an audit trail to be produced. */  
  
UPDATE dbo.employeeData  
   SET emp_bankAccountNumber = '133146A0', emp_SSN = 'R-M53550M'  
   WHERE emp_id = 101;  
GO  
SELECT * FROM dbo.auditEmployeeData;  
  
GO

B. Using COLUMNS_UPDATED to test more than eight columns

To test for updates that affect columns other than the first eight table columns, use the SUBSTRING function to test the correct bit returned by COLUMNS_UPDATED. This example tests for updates affecting columns 3, 5, and 9 in the AdventureWorks2022.Person.Person table.

USE AdventureWorks2022;  
GO  
IF OBJECT_ID (N'Person.uContact2', N'TR') IS NOT NULL  
    DROP TRIGGER Person.uContact2;  
GO  
CREATE TRIGGER Person.uContact2 ON Person.Person  
AFTER UPDATE AS  
    IF ( (SUBSTRING(COLUMNS_UPDATED(), 1, 1) & 20 = 20)   
        AND (SUBSTRING(COLUMNS_UPDATED(), 2, 1) & 1 = 1) )   
    PRINT 'Columns 3, 5 and 9 updated';  
GO  
  
UPDATE Person.Person   
   SET NameStyle = NameStyle,  
      FirstName=FirstName,  
      EmailPromotion=EmailPromotion;  
GO

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