Index schema
Index name
Table schema
Table name
Available columns
Selected columns
Include columns
Unique
Cluster
Allow reverse scans
Percentage of free space to be left on index
pages
Percentage of minimum amount of used space to be left
on index pages
Comment
Ascending and Descending
Up
Down
OK
Cancel
Show SQL
Estimate Size
Index schema
This field specifies the schema of the index that you are altering. This is a read-only field.
Index name
This field specifies the name of the index that you are altering. This is a read-only field.
Table schema
This field specifies the schema of the table that you are altering. This is a read-only field.
Table name
This field specifies the table on which the index that you are altering was created. This is a read-only field.
Available columns
This list box lists all of the columns defined for the table specified in the Table name field. This is a read-only field.
Selected columns
This box specifies the column or columns that were defined as part of the index key when the index you are altering was created. This is a read-only field.
Ascending and Descending
These radio buttons indicate the sort order of the columns in the Selected columns list box. These are a read-only fields.
Unique
If a check appears in this check box it indicates that a table does not contain two or more rows with the same value of the index key. This is a read-only field.
When the Unique check box is selected, null values are treated as any other values. For example, if the key is a single column that can contain null values, that column can contain no more than one null value.
Cluster
If a check appears in this check box it indicates that the index is the clustering index of the table. This is a read-only field.
Allow reverse scans
If a check appears in this check box it indicates that Reverse scans can be performed on the index that you are altering. This is a read-only field.
When the check box is checked, the index can support both forward and reverse scans; that is, the scan can be performed in the order defined at INDEX CREATE time and in the opposite (or reverse) order. This eliminates the need for the optimizer to create a temporary table for a reverse scan and it eliminates the need for you to create 2 indexes for the same columns on the table, one for forward and one for reverse scanning. It also facilitates determination of the maximum key of an index.
When the check box is not checked, the index only supports forward scans or scanning of the index in the order defined at INDEX CREATE time.
Percentage of free space to be left on index pages
This field specifies the percentage of each index page that will be left as free space when building the index. This is a read-only field.
The first entry in a page is added without restriction. When additional entries are placed in an index page, the value specified in this field determines the percentage of free space left on each page.
The value can be from 0 to 99 percent. The default value is 10 percent. If a value greater than 10 has been selected, only 10 percent free space will be left in non-leaf pages.
Percentage of minimum amount of used space to be left on index
pages
This field specifies for, Online Index Reorganization, the threshold for the minimum percentage of used space on an index leaf page. If the percentage of space used on the page is at or below integer % after a key is deleted from an index leaf page, an attempt will be made to merge the remaining keys on this page with those of a neighbouring page. If there's sufficient space on one of these pages, the merge will be performed and one of the pages will be deleted.
The value of integer can be from 0 to 99. However, a value of 50 or below is recommended for performance reasons. The default value is 10 percent.
Comment
Type a comment to document the index that you are creating. You can type up to 254 characters, including embedded blanks.
Include columns
This box specifies additional columns that are included in the index that are not part of the unique index key. These columns may improve the performance of some queries through index-only access.The columns are distinct from the columns used to enforce uniqueness.
Estimate Size
Click on this push button to open the Estimate Size window, in which you can estimate the amount of storage space for a new or existing table or index.
