Using Wildcards in Queries
Wildcards Behavior
Wildcard characters: * and ?
When you use a wildcard syntax in the search box, the Coveo Platform expands keywords containing wildcard characters to the possible matching keywords to broaden the query.
Examples:
micro*
Could match Microsoft and microprocessor.
te?t
Could return documents containing either the words text or test but could also documents containing te4t when this term exists in indexed documents.
Note: This works only when the question mark wildcard behavior is enabled (see Enabling the Question Mark Wildcard Behavior in a .NET Search Interface).
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Matching a pattern
Using wildcards can be useful when you do not remember the exact spelling for the name of a person, company, or product but you do remember part of it.
Using wildcard characters can be useful when you want to match all variants of a pattern. You type the fixed part of the pattern and use a wildcard character to expand to the variants.
Example:
THI10*
Find all product names starting with THI10.
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Wildcard in a phrase search
You can use wildcard characters within an exact match phrase, allowing some variability in a phrase search.
Example:"fina* scandals 201?"
Returns documents containing the following phrases:
- financial scandals 2012
- final scandals 2010
Note: This works only when the question mark wildcard behavior is enabled (see Enabling the Question Mark Wildcard Behavior in a .NET Search Interface).
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Wildcard with the NEAR operator
You can also use wildcard characters with the NEAR operator.
Example:
Fina* NEAR scandals
Returns documents containing occurrences of words starting with fina that are within ten words from the word scandals.
Wildcard Constraints
Wildcard queries can significantly expand a query and consequently consume significantly more server resources than a typical query.
To prevent this:
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By default at least two leading characters must precede the wildcard to restrict the number of wildcard terms candidates. Thus, it is not supported to begin with a wildcard.
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The query expansion is limited by default to the first 32 wildcard terms found alphabetically.
Note: Your Coveo administrator can customize the wildcard Number of candidates and Number of Leading Chars parameters to change these restrictions (see Modifying or Using Advanced Index Parameters).
Tip: Wildcard queries on the entire content of an index will always take longer to return results. For content where wildcards are appropriate, consider isolating the data in a field, and using the field for the wildcard search. When searching in a field, the number of possibilities is smaller, so using the same wildcard expression may return more or even all possible results (see What Are Field Queries and Free Text Queries?).