Retrieving data values using b$, a$, k$, and d$ prefixes

The b$, a$, k$, and d$ prefixes are used to retrieve data.

The following prefixes are available:

Prefix Mode Description
b$<source column name> Input

Used to retrieve the before image of the data in a source column. The before image is the original image from the source table column before any transformation is applied to it.

For example, you may have made the following UPDATE to your source table:

UPDATE source_table 
set MYCOLUMN = 2 
where MYCOLUMN = 1;

This will set 2 on all rows where MYCOLUMN was 1 before the execution of this SQL statement.

When you define a stored procedure and decide that you want the stored procedure to retrieve the before image of MYCOLUMN, you would specify the following:

b$MYCOLUMN;

This returns a value of 1.
a$<source column name> Input

Used to retrieve the after image of the data in a source column. The after image is the translated data from the source table column. For example, the data that was translated by a derived expression.

For example, you may have made the following UPDATE to your source table:

UPDATE source_table 
set MYCOLUMN = 2 
where MYCOLUMN = 1;

This will set 2 on all rows where MYCOLUMN was 1 before the execution of this SQL statement.

When you define a stored procedure and decide that you want the stored procedure to retrieve the after image of MYCOLUMN, you would specify the following:

a$MYCOLUMN;

This returns a value of 2.
k$<target key column name> Input Used to access the target table to find the rows that need to be modified.
Note: Key columns are not available for auditing.
d$<target column name> Input/Output Used to retrieve data values after transformation, which will be used to update the table in the target database. Only these values may be modified by the stored procedure.