tAddCRCRow returns duplicate values for different inputs

[RahulReliable]

Background: In talend Data Management studio, We are loading data to multiple tables and in each table we are using taddCRCRow for one of our common column. 
later we are joining these tables based on this column in database as per our client's requirement.

issue : in a table , we have different values to our columns. when we are connecting it to tAddCRCRow,  we are getting same results for two columns three times. 

If my column have different values , it should return different CRC value as well ?
please advice.

[Rahul_Kale]

Hello RahulReliable,

Thank you for reaching out to the Qlik community.
 

tAddCRCRow does not guarantee unique values. It computes a CRC (hash) from the selected columns, and different inputs can legitimately produce the same CRC (called a collision), especially if:

• You selected only one column or too few columns,
• you are using a short CRC type (CRC8/CRC16),
• values differ only by spaces, case, or trimming rules, or
• The data size is large.

So, different column values do NOT always mean different CRC values by design.

To deal with this, we recommend the following.

• Select all business key columns that define uniqueness (not just one). document.
• Use CRC32 (longer CRC → fewer collisions). 
• Normalize data first (TRIM, UPPER/LOWER) before tAddCRCRow. document.
• Do NOT rely on CRC as a guaranteed join key—use it only as a helper checksum.