Recommended Use of WD

Use a WD index for the fastest access to columns that contain a list of keywords (for example, in a bibliographic record or Web page).

These restrictions apply to WD indexes:

You cannot specify the UNIQUE attribute.
It can be used only with the CONTAINS or LIKE predicate.
The column-name must identify a CHAR, VARCHAR, or LONG VARCHAR column in a base table.
The minimum permitted column width is 3 bytes and the maximum permitted column width is the maximum width for a LOB column. (The maximum length is equal to 4GB multiplied by the database page size.)
You must enclose the list of delimiters in single quotes.
You omit the DELIMITED BY clause or specify the separators-string value as empty (single quotes), then SAP Sybase IQ uses the default set of separators. The default set of characters includes all 7-bit ASCII characters that are not 7-bit ASCII alphanumeric characters, except the hyphen and the single quotation mark, which, by default, are part of words. There are 64 separators in the default separator set.
If you specify multiple DELIMITED BY and LIMIT clauses, no error is returned, but only the last clause of each type is used. For example, the following two statements return identical results:
Statement 1:
```
CREATE WD INDEX c1wd on foo(c1)
DELIMITED BY 'f' LIMIT 40 LIMIT 99 DELIMITED BY 'g' DELIMITED BY 'h';
```
Statement 2:
```
CREATE WD INDEX c1wd on foo(c1)
DELIMITED BY 'h' LIMIT 99;
```
After a WD index is created, any insertions into its column are parsed using the separators and maximum word size cannot be changed after the index is created.
For CHAR columns, Specify a space as at least one of the separators or use the default separator set. SAP Sybase IQ automatically pads CHAR columns to the maximum column width. If your column contains blanks in addition to the character data, queries on WD indexed data may return misleading results. For example, column company_name contains two words delimited by a separator, but the second word is blank padded:
```
'Concord' 'Farms										 '
```
Suppose that a user entered the following query:
```
SELECT COUNT(*)FROM Customers WHERE CompanyName contains ('Farms')
```
The parser determines that the string contains:
```
'Farms										 '
```
instead of:
```
'Farms'
```
and returns 1. You can avoid this problem by using VARCHAR instead of CHAR columns.
The sp_iqcheckdb (DBCC consistency checker) allocation, check, verify, and repair modes support the WD index on CHAR, VARCHAR, and LONG VARCHAR columns.