SYSIXCOL system table

CREATE TABLE SYS.SYSIXCOL (
	table_id	 UNSIGNED INT NOT NULL,
	index_id	 UNSIGNED INT NOT NULL,
	sequence	 SMALLINT NOT NULL,
	column_id	 UNSIGNED INT NOT NULL,
	"order" CHAR(1) NOT NULL,
	PRIMARY KEY ( table_id, index_id, sequence ),
	FOREIGN KEY REFERENCES SYS.SYSINDEX,
	FOREIGN KEY REFERENCES SYS.SYSCOLUMN
)

Every index has one row in SYSIXCOL for each column in the index.

table_id Identifies the table to which the index applies.

index_id Identifies in which index this column is used. Together, table_id and index_id identify one index described in SYSINDEX.

sequence Each column in an index is assigned a unique number starting at 0. The order of these numbers determines the relative significance of the columns in the index. The most important column has sequence number 0.

column_id The column number identifies which column is indexed. Together, table_id and column_id identify one column in SYSCOLUMN.

“order” Indicates whether this column in the index is kept in ascending or descending order (A or D).