Sybase 12.4.2 manual Issuing the Create Join Index statement, Parameters of this command are, 162

Using join indexes

•Use parentheses to control the order in which the join relationships are evaluated. Parentheses control evaluation order just as they do in mathematics, that is, innermost pairs are evaluated first. With this method you start with the top table in the outermost set of parentheses, then any intermediate levels, and include the lowest two levels in the innermost parentheses. Using this method, you would specify the same three tables as follows:

(F FULL OUTER JOIN (C FULL OUTER JOIN E))

Note that the lowest level table appears first in the innermost parentheses, just as it does in the first method.

Note While you can join these three tables in the way described here, in order to create the complete hierarchy shown in Figure 4-1 you would need to use key joins. See “Types of join hierarchies” for more information.

When you create a join index, a message in the log identifies the top table in the join. For example,

[20691]: Join Index ’join_on_tabletable’ created from the following join relations:

[20694]:	Table Name	Relationship
[20697]:	------------------------------------------------------------------
[20696]: 1. join_on_table_a joined		to ’join_on_table_b’ One >> Many
[20692]: The ultimate/top table is		join_on_table_b
[20697]:	------------------------------------------------------------------

Issuing the CREATE JOIN INDEX statement

To create a join index, issue the CREATE JOIN INDEX statement. Here is a summary of the syntax for this command:

CREATE JOIN INDEX join-index-name FOR join-clause

The parameters of this command are:

join-clause:

[ ( ] join-expression join-type join-expression [ ON search-condition ] [ ) ]

join-expression:

{table-name join-clause }

join-type:

[ NATURAL ] FULL [ OUTER ] JOIN

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