You can compress a set of join index column values that repeat often across rows. This is referred to as row compression. Group the columns with values that do not repeat frequently. This non-repeating column set is called the fixed column set. Then, group the columns with repeating values.
You can configure row compression for a join index. In the join index definition, group the fixed set of columns in parenthesis, then group the set of repeating columns in parenthesis, separating the two groups with a COMMA character.
The join index t3_jindx in Example: Creating Join Indexes With a UDT Column as a Primary or Secondary Index is a simple example of how to create a row-compressed join index.
For a detailed explanation of join index row compression, see “Row Compression of Join Indexes” in SQL Data Definition Language - Detailed Topics, B035-1184.
You cannot specify row compression for a partitioned join index.