Simple query syntax in Azure AI Search

บทความ
08/28/2024

For full text search scenarios, Azure AI Search implements two Lucene-based query languages, each one aligned to a query parser. The Simple Query Parser is the default. It covers common use cases and attempts to interpret a request even if it's not perfectly composed. The other parser is Lucene Query Parser and it supports more advanced query constructions.

This article is the query syntax reference for the simple query parser.

Query syntax for both parsers applies to query expressions passed in the search parameter of a query request, not to be confused with the OData syntax, with its own syntax and rules for filter and orderby expressions in the same request.

Although the simple parser is based on the Apache Lucene Simple Query Parser class, its implementation in Azure AI Search excludes fuzzy search. If you need fuzzy search, consider the alternative full Lucene query syntax instead.

Example (simple syntax)

This example shows a simple query, distinguished by "queryType": "simple" and valid syntax. Although query type is set below, it's the default and can be omitted unless you're reverting from an alternative type. The following example is a search over independent terms, with a requirement that all matching documents include "pool".

POST https://{{service-name}}.search.windows.net/indexes/hotel-rooms-sample/docs/search?api-version=2024-07-01
{
  "queryType": "simple",
  "search": "budget hotel +pool",
  "searchMode": "all"
}

The searchMode parameter is relevant in this example. Whenever boolean operators are on the query, you should generally set searchMode=all to ensure that all of the criteria are matched. Otherwise, you can use the default searchMode=any that favors recall over precision.

For more examples, see Simple query syntax examples. For details about the query request and parameters, see Search Documents (REST API).

Keyword search on terms and phrases

Strings passed to the search parameter can include terms or phrases in any supported language, boolean operators, precedence operators, wildcard or prefix characters for "starts with" queries, escape characters, and URL encoding characters. The search parameter is optional. Unspecified, search (search=* or search=" ") returns the top 50 documents in arbitrary (unranked) order.

A term search is a query of one or more terms, where any of the terms are considered a match.
A phrase search is an exact phrase enclosed in quotation marks " ". For example, while Roach Motel (without quotes) would search for documents containing Roach and/or Motel anywhere in any order, "Roach Motel" (with quotes) will only match documents that contain that whole phrase together and in that order (lexical analysis still applies).

Depending on your search client, you might need to escape the quotation marks in a phrase search. For example, in a POST request, a phrase search on "Roach Motel" in the request body might be specified as "\"Roach Motel\"". If you're using the Azure SDKs, the search client escapes the quotation marks when it serializes the search text. Your search phrase can be sent be as "Roach Motel".

By default, all strings passed in the search parameter undergo lexical analysis. Make sure you understand the tokenization behavior of the analyzer you're using. Often, when query results are unexpected, the reason can be traced to how terms are tokenized at query time. You can test tokenization on specific strings to confirm the output.

Any text input with one or more terms is considered a valid starting point for query execution. Azure AI Search will match documents containing any or all of the terms, including any variations found during analysis of the text.

As straightforward as this sounds, there's one aspect of query execution in Azure AI Search that might produce unexpected results, increasing rather than decreasing search results as more terms and operators are added to the input string. Whether this expansion actually occurs depends on the inclusion of a NOT operator, combined with a searchMode parameter setting that determines how NOT is interpreted in terms of AND or OR behaviors. For more information, see the NOT operator under Boolean operators.

Boolean operators

You can embed Boolean operators in a query string to improve the precision of a match. In the simple syntax, boolean operators are character-based. Text operators, such as the word AND, aren't supported.

Character Example Usage

+ pool + ocean An AND operation. For example, pool + ocean stipulates that a document must contain both terms.

| pool | ocean An OR operation finds a match when either term is found. In the example, the query engine will return a match on documents containing either pool or ocean or both. Because OR is the default conjunction operator, you could also leave it out, such that pool ocean is the equivalent of pool | ocean.

Character	Example	Usage
`+`	`pool + ocean`	An `AND` operation. For example, `pool + ocean` stipulates that a document must contain both terms.
`\|`	`pool \| ocean`	An `OR` operation finds a match when either term is found. In the example, the query engine will return a match on documents containing either `pool` or `ocean` or both. Because `OR` is the default conjunction operator, you could also leave it out, such that `pool ocean` is the equivalent of `pool \| ocean`.
`-`	`pool – ocean`	A `NOT` operation returns matches on documents that exclude the term. The `searchMode` parameter on a query request controls whether a term with the `NOT` operator is `AND`ed or `OR`ed with other terms in the query (assuming there's no boolean operators on the other terms). Valid values include `any` or `all`. `searchMode=any` increases the recall of queries by including more results, and by default `-` will be interpreted as "OR NOT". For example, `pool - ocean` will match documents that either contain the term `pool` or those that don't contain the term `ocean`. `searchMode=all` increases the precision of queries by including fewer results, and by default `-` will be interpreted as "AND NOT". For example, with `searchMode=any`, the query `pool - ocean` will match documents that contain the term "pool" and all documents that don't contain the term "ocean". This is arguably a more intuitive behavior for the `-` operator. Therefore, you should consider using `searchMode=all` instead of `searchMode=any` if you want to optimize searches for precision instead of recall, and Your users frequently use the `-` operator in searches. When deciding on a `searchMode` setting, consider the user interaction patterns for queries in various applications. Users who are searching for information are more likely to include an operator in a query, as opposed to e-commerce sites that have more built-in navigation structures.

-

pool – ocean

A NOT operation returns matches on documents that exclude the term.

The searchMode parameter on a query request controls whether a term with the NOT operator is ANDed or ORed with other terms in the query (assuming there's no boolean operators on the other terms). Valid values include any or all.

searchMode=any increases the recall of queries by including more results, and by default - will be interpreted as "OR NOT". For example, pool - ocean will match documents that either contain the term pool or those that don't contain the term ocean.

searchMode=all increases the precision of queries by including fewer results, and by default - will be interpreted as "AND NOT". For example, with searchMode=any, the query pool - ocean will match documents that contain the term "pool" and all documents that don't contain the term "ocean". This is arguably a more intuitive behavior for the - operator. Therefore, you should consider using searchMode=all instead of searchMode=any if you want to optimize searches for precision instead of recall, and Your users frequently use the - operator in searches.

When deciding on a searchMode setting, consider the user interaction patterns for queries in various applications. Users who are searching for information are more likely to include an operator in a query, as opposed to e-commerce sites that have more built-in navigation structures.

Prefix queries

For "starts with" queries, add a suffix operator (*) as the placeholder for the remainder of a term. A prefix query must begin with at least one alphanumeric character before you can add the suffix operator.

Character	Example	Usage
`*`	`lingui*` will match on "linguistic" or "linguini"	The asterisk (`*`) represents one or more characters of arbitrary length, ignoring case.

Similar to filters, a prefix query looks for an exact match. As such, there's no relevance scoring (all results receive a search score of 1.0). Be aware that prefix queries can be slow, especially if the index is large and the prefix consists of a small number of characters. An alternative methodology, such as edge n-gram tokenization, might perform faster. Terms using prefix search can't be longer than 1000 characters.

Simple syntax supports prefix matching only. For suffix or infix matching against the end or middle of a term, use the full Lucene syntax for wildcard search.

Escaping search operators

In the simple syntax, search operators include these characters: + | " ( ) ' \

If any of these characters are part of a token in the index, escape it by prefixing it with a single backslash (\) in the query. For example, suppose you used a custom analyzer for whole term tokenization, and your index contains the string "Luxury+Hotel". To get an exact match on this token, insert an escape character: search=luxury\+hotel.

To make things simple for the more typical cases, there are two exceptions to this rule where escaping isn't needed:

The NOT operator - only needs to be escaped if it's the first character after a whitespace. If the - appears in the middle (for example, in 3352CDD0-EF30-4A2E-A512-3B30AF40F3FD), you can skip escaping.
The suffix operator * only needs to be escaped if it's the last character before a whitespace. If the * appears in the middle (for example, in 4*4=16), no escaping is needed.

Note

By default, the standard analyzer will delete and break words on hyphens, whitespace, ampersands, and other characters during lexical analysis. If you require special characters to remain in the query string, you might need an analyzer that preserves them in the index. Some choices include Microsoft natural language analyzers, which preserves hyphenated words, or a custom analyzer for more complex patterns. For more information, see Partial terms, patterns, and special characters.

Encoding unsafe and reserved characters in URLs

Ensure all unsafe and reserved characters are encoded in a URL. For example, '#' is an unsafe character because it's a fragment/anchor identifier in a URL. The character must be encoded to %23 if used in a URL. '&' and '=' are examples of reserved characters as they delimit parameters and specify values in Azure AI Search. For more information, see RFC1738: Uniform Resource Locators (URL).

Unsafe characters are " ` < > # % { } | \ ^ ~ [ ]. Reserved characters are ; / ? : @ = + &.

Special characters

Special characters can range from currency symbols like '$' or '€', to emojis. Many analyzers, including the default standard analyzer, will exclude special characters during indexing, which means they won't be represented in your index.

If you need special character representation, you can assign an analyzer that preserves them:

The whitespace analyzer considers any character sequence separated by white spaces as tokens (so the '❤' emoji would be considered a token).
A language analyzer, such as the Microsoft English analyzer (en.microsoft), would take the '$' or '€' string as a token.

For confirmation, you can test an analyzer to see what tokens are generated for a given string. As you might expect, you might not get full tokenization from a single analyzer. A workaround is to create multiple fields that contain the same content, but with different analyzer assignments (for example, description_en, description_fr, and so forth for language analyzers).

When using Unicode characters, make sure symbols are properly escaped in the query url (for instance for '❤' would use the escape sequence %E2%9D%A4+). Some web clients do this translation automatically.

Precedence (grouping)

You can use parentheses to create subqueries, including operators within the parenthetical statement. For example, motel+(wifi|luxury) will search for documents containing the "motel" term and either "wifi" or "luxury" (or both).

Query size limits

If your application generates search queries programmatically, we recommend designing it in such a way that it doesn't generate queries of unbounded size.

For GET, the length of the URL can't exceed 8 KB.
For POST (and any other request), where the body of the request includes search and other parameters such as filter and orderby, the maximum size is 16 MB. Additional limits include:
- The maximum length of the search clause is 100,000 characters.
- The maximum number of clauses in search (expressions separated by AND or OR) is 1024.
- The maximum search term size is 1000 characters for prefix search.
- There's also a limit of approximately 32 KB on the size of any individual term in a query.

For more information on query limits, see API request limits.

Next steps

If you'll be constructing queries programmatically, review Full text search in Azure AI Search to understand the stages of query processing and the implications of text analysis.

You can also review the following articles to learn more about query construction:

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