Sybase 12.4.2 manual Join hierarchy in query resolution, One-to-many relationship, 154

Using join indexes

You can set the frequency of these messages with the NOTIFY_MODULUS option, and override the option value in either the CREATE DATABASE or LOAD TABLE command. For examples of these messages, see “Interpreting notification messages” on page 187.

The join hierarchy in query resolution

Adaptive Server IQ can use the same join index to resolve a query that involves the full join relationship specified in the join index, or a query that involves any contiguous subset of that relationship; you do not have to create separate join indexes for the subset relationships.

For example, assume that join index ABCDEF joins the tables illustrated in Figure 4-1. Adaptive Server IQ can use join index ABCDEF to resolve any queries that involve:

•The entire relationship

•Table A to Table D

•Table A to Table D to Table F

•Table B to Table D

•Table B to Table D to Table F

•Table D to Table F

•Table C to Table E

•Table E to Table F

•Table C to Table E to Table F

However, Adaptive Server IQ cannot use join index ABCDEF to resolve queries against, for example, Table E to Table D.

One-to-many relationship

In a one-to-many join relationship, one row in one table potentially matches with one or more rows in another table, and there is not more than one row in the first table that matches with the same row(s) in the second table. For this to be true, the values in the join column in the first table must be unique.

It is possible that either table has no match on the other table. This constitutes an outer join and is fully supported. For more information, see the Introduction to Adaptive Server IQ.

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