ER/Studio - Embarcadero Technologies Product Documentation

USING ER/STUDIO > DEVELOPING THE PHYSICAL MODEL
Edit an Index
1 In the Data Model Explorer, expand the Index node of a physical data model, and then double-click the index
you want to change.
TIP: You can also edit an index on the Index tab of the Table Editor for the table to which the index
belongs.
2 Complete the Index Editor as required and then click OK.
TIP: If you change the index options and can see no reflection of the change in the DDL, click
Customize on the DDL tab and ensure the options required to display your changes are selected.
For example, If you create a non-unique index for a MySQL table and turn on full text, you must
customize the DDL by selecting Generate Defined Nonunique Indexes for the index to show up.
The following describe options that require additional explanation.
NOTE: The options and tabs available depend on the database platform.
• Set as PK Index: Read-only. If selected, indicates that the index selected is the primary key.
• Unique Constraint: Select to specify that every value in the named column must be unique. Unique constraints
are similar to Primary keys. They require unique values throughout the named column or columns in the table.
• Physical Only: Select to specify that the index be ignored when comparing the physical model to a logical
model.
For information on the various tabs available, click a link below:
• Columns tab
• Properties tab
• Options tab
• Storage tab
• Partitions tab
• Compare Options tab
• Attachment Bindings tab
Columns tab
Select the columns or keys, the index should be based on. The efficiency of the index depends upon the keys
chosen and their search order.
Properties tab
This tab is available for Oracle 8.x, 9i, 10g, and 11g.
• Index Type: Select the appropriate index type; it can have a big impact on performance.
• Bitmap: Select for an index that will not be frequently updated by concurrent applications, although be aware
that when applied to the index of a unique column (primary key candidate) you need to consider the space
required, which depends on the cardinality of the column and the data distribution. A bitmap for each key value
is used instead of a list of row IDs.
• B-tree: Select when indexing a primary key, because Oracle does not support primary key indexes, or select
B-tree when space is a consideration. B-tree indexes are balanced to equalize access times to any row.
• Unique: (UNIQUE) If selected, specifies that the index key contains no duplicate values and therefore every row
in the table is in some way unique. If not selected, a non-unique index is created that lets table rows have
duplicate values in the columns that define the index. For a unique index, there is one rowid per data value. If
selected, Oracle will generate a separate unique index before creating the PK constraint.
EMBARCADERO TECHNOLOGIES > ER/STUDIO® 8.0.3 USER GUIDE 167