Oracle Cloud Infrastructure Documentation

Random Substitution


The Random Substitution masking format enables you to mask values in a column using data from a substitution column. The values in the user-specified column are randomly ordered before mapping them to the original column values.


  • Schema Name: The name of the schema containing the substitution column
  • Table Name: The name of the table containing the substitution column
  • Column Name: The name of the substitution column containing the data that should be used for masking. The data types of the specified substitution column and column to be matched must be the same.

Supported Data Types

  • Character
  • Numeric
  • Date


  • Combinable: No
  • Deterministic: No, because the Random Substitution masking format randomly orders the mask values in the substitution column before replacing the sensitive data (unlike the Deterministic Substitution masking format)
  • Reversible: No
  • Uniqueness: Yes. The number of distinct values in the substitution column must be greater than or equal to the number of values in the column to be masked.


Suppose you discover a sensitive column named EMP_ID that contains employee IDs. Let's assume that you have fake employee ID values stored in another column named SUB_EMP_ID, which resides in the SUB_EMPLOYEES table in the SUB_HR schema (as shown in the following table).









When configuring the masking policy in the Data Masking wizard, you can choose the Random Substitution masking format for the EMP_ID column. Provide the following inputs: SUB_HR, SUB_EMPLOYEES, and SUB_EMP_ID. When the job runs, Data Masking randomly orders the fake values in the SUB_EMP_ID column and uses them to replace the values in the EMP_ID column.

The following table compares the values in the original column (EMP_ID) to the values after the first masking job (MASK1) and second masking job (MASK2). Notice that the masked values change each time the masking job runs.

412 101 104
185 107 105
102 105 102
322 102 101
692 103 106