You must specify two or more column names to create a composite index on the combined values in all the specified columns.
Use composite indexes when two or more columns are best searched as a unit, for example, the first and last names of authors in the authors table. List the columns to be included in the composite index in sort-priority order, inside the parentheses after the table name, like this:
create index auth_name_ind on authors(au_fname, au_lname)
The columns in a composite index do not have to be in the same order as the columns in the create table statement. For example, the order of au_lname and au_fname could be reversed in the preceding index creation statement.
You can specify up to 31 columns in a single composite index in Adaptive Server 11.9.2 and later. All the columns in a composite index must be in the same table. For the maximum allowable size of the combined index values, see Table 1-6: Maximum index row size, in the Reference Manual: Vol.1, Commands.
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