Elasticsearch Query String Query

Query String Queryedit

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• Query string syntax

A query that uses a query parser in order to parse its content. Here is an example:

{
    "query_string" : {
        "default_field" : "content",
        "query" : "this AND that OR thus"
    }
}

The query_string top level parameters include:

Parameter	Description
query	The actual query to be parsed. See Query string syntax.
default_field	The default field for query terms if no prefix field is specified. Defaults to the index.query.default_field index settings, which in turn defaults to_all.
default_operator	The default operator used if no explicit operator is specified. For example, with a default operator of OR, the query capital of Hungary is translated tocapital OR of OR Hungary, and with default operator of AND, the same query is translated to capital AND of AND Hungary. The default value is OR.
analyzer	The analyzer name used to analyze the query string.
allow_leading_wildcard	When set, * or ? are allowed as the first character. Defaults to true.
lowercase_expanded_terms	Whether terms of wildcard, prefix, fuzzy, and range queries are to be automatically lower-cased or not (since they are not analyzed). Default ittrue.
enable_position_increments	Set to true to enable position increments in result queries. Defaults totrue.
fuzzy_max_expansions	Controls the number of terms fuzzy queries will expand to. Defaults to 50
fuzziness	Set the fuzziness for fuzzy queries. Defaults to AUTO. See the section called “Fuzzinessedit” for allowed settings.
fuzzy_prefix_length	Set the prefix length for fuzzy queries. Default is 0.
phrase_slop	Sets the default slop for phrases. If zero, then exact phrase matches are required. Default value is 0.
boost	Sets the boost value of the query. Defaults to 1.0.
analyze_wildcard	By default, wildcards terms in a query string are not analyzed. By setting this value to true, a best effort will be made to analyze those as well.
auto_generate_phrase_queries	Defaults to false.
max_determinized_states	Limit on how many automaton states regexp queries are allowed to create. This protects against too-difficult (e.g. exponentially hard) regexps. Defaults to 10000.
minimum_should_match	A value controlling how many "should" clauses in the resulting boolean query should match. It can be an absolute value (2), a percentage (30%) or acombination of both.
lenient	If set to true will cause format based failures (like providing text to a numeric field) to be ignored.
locale	Locale that should be used for string conversions. Defaults to ROOT.
time_zone	Time Zone to be applied to any range query related to dates. See also JODA timezone.

When a multi term query is being generated, one can control how it gets rewritten using the rewriteparameter.

Default Fieldedit

When not explicitly specifying the field to search on in the query string syntax, theindex.query.default_field will be used to derive which field to search on. It defaults to _all field.

So, if _all field is disabled, it might make sense to change it to set a different default field.

Multi Fieldedit

The query_string query can also run against multiple fields. Fields can be provided via the "fields"parameter (example below).

The idea of running the query_string query against multiple fields is to expand each query term to an OR clause like this:

field1:query_term OR field2:query_term | ...

For example, the following query

{
    "query_string" : {
        "fields" : ["content", "name"],
        "query" : "this AND that"
    }
}

matches the same words as

{
    "query_string": {
      "query": "(content:this OR name:this) AND (content:that OR name:that)"
    }
}

Since several queries are generated from the individual search terms, combining them can be automatically done using either a dis_max query or a simple bool query. For example (the name is boosted by 5 using ^5notation):

{
    "query_string" : {
        "fields" : ["content", "name^5"],
        "query" : "this AND that OR thus",
        "use_dis_max" : true
    }
}

Simple wildcard can also be used to search "within" specific inner elements of the document. For example, if we have a city object with several fields (or inner object with fields) in it, we can automatically search on all "city" fields:

{
    "query_string" : {
        "fields" : ["city.*"],
        "query" : "this AND that OR thus",
        "use_dis_max" : true
    }
}

Another option is to provide the wildcard fields search in the query string itself (properly escaping the *sign), for example: city.\*:something.

When running the query_string query against multiple fields, the following additional parameters are allowed:

Parameter	Description
use_dis_max	Should the queries be combined using dis_max (set it to true), or a bool query (set it tofalse). Defaults to true.
tie_breaker	When using dis_max, the disjunction max tie breaker. Defaults to 0.

The fields parameter can also include pattern based field names, allowing to automatically expand to the relevant fields (dynamically introduced fields included). For example:

{
    "query_string" : {
        "fields" : ["content", "name.*^5"],
        "query" : "this AND that OR thus",
        "use_dis_max" : true
    }
}

Query string syntaxedit

The query string “mini-language” is used by the Query String Query and by the q query string parameter in the search API.

The query string is parsed into a series of terms and operators. A term can be a single word — quick orbrown — or a phrase, surrounded by double quotes — "quick brown" — which searches for all the words in the phrase, in the same order.

Operators allow you to customize the search — the available options are explained below.

Field namesedit

As mentioned in Query String Query, the default_field is searched for the search terms, but it is possible to specify other fields in the query syntax:

• where the status field contains active

  status:active

• where the title field contains quick or brown. If you omit the OR operator the default operator will be used

  title:(quick OR brown)
  title:(quick brown)

• where the author field contains the exact phrase "john smith"

  author:"John Smith"

• where any of the fields book.title, book.content or book.date contains quick or brown (note how we need to escape the * with a backslash):

  book.\*:(quick brown)

• where the field title has no value (or is missing):

  _missing_:title

• where the field title has any non-null value:

  _exists_:title

Wildcardsedit

Wildcard searches can be run on individual terms, using ? to replace a single character, and * to replace zero or more characters:

qu?ck bro*

Be aware that wildcard queries can use an enormous amount of memory and perform very badly — just think how many terms need to be queried to match the query string "a* b* c*".

Allowing a wildcard at the beginning of a word (eg "*ing") is particularly heavy, because all terms in the index need to be examined, just in case they match. Leading wildcards can be disabled by setting allow_leading_wildcard to false.

Wildcarded terms are not analyzed by default — they are lowercased (lowercase_expanded_terms defaults totrue) but no further analysis is done, mainly because it is impossible to accurately analyze a word that is missing some of its letters. However, by setting analyze_wildcard to true, an attempt will be made to analyze wildcarded words before searching the term list for matching terms.

Regular expressionsedit

Regular expression patterns can be embedded in the query string by wrapping them in forward-slashes ("/"):

name:/joh?n(ath[oa]n)/

The supported regular expression syntax is explained in Regular expression syntax.

The allow_leading_wildcard parameter does not have any control over regular expressions. A query string such as the following would force Elasticsearch to visit every term in the index:

/.*n/

Use with caution!

Fuzzinessedit

We can search for terms that are similar to, but not exactly like our search terms, using the “fuzzy” operator:

quikc~ brwn~ foks~

This uses the Damerau-Levenshtein distance to find all terms with a maximum of two changes, where a change is the insertion, deletion or substitution of a single character, or transposition of two adjacent characters.

The default edit distance is 2, but an edit distance of 1 should be sufficient to catch 80% of all human misspellings. It can be specified as:

quikc~1

Proximity searchesedit

While a phrase query (eg "john smith") expects all of the terms in exactly the same order, a proximity query allows the specified words to be further apart or in a different order. In the same way that fuzzy queries can specify a maximum edit distance for characters in a word, a proximity search allows us to specify a maximum edit distance of words in a phrase:

"fox quick"~5

The closer the text in a field is to the original order specified in the query string, the more relevant that document is considered to be. When compared to the above example query, the phrase "quick fox" would be considered more relevant than "quick brown fox".

Rangesedit

Ranges can be specified for date, numeric or string fields. Inclusive ranges are specified with square brackets [min TO max] and exclusive ranges with curly brackets {min TO max}.

• All days in 2012:

  date:[2012-01-01 TO 2012-12-31]

• Numbers 1..5

  count:[1 TO 5]

• Tags between alpha and omega, excluding alpha and omega:

  tag:{alpha TO omega}

• Numbers from 10 upwards

  count:[10 TO *]

• Dates before 2012

  date:{* TO 2012-01-01}

Curly and square brackets can be combined:

• Numbers from 1 up to but not including 5

  count:[1 TO 5}

Ranges with one side unbounded can use the following syntax:

age:>10
age:>=10
age:<10
age:<=10

To combine an upper and lower bound with the simplified syntax, you would need to join two clauses with an AND operator:

age:(>=10 AND <20)
age:(+>=10 +<20)

The parsing of ranges in query strings can be complex and error prone. It is much more reliable to use an explicit range query.

Boostingedit

Use the boost operator ^ to make one term more relevant than another. For instance, if we want to find all documents about foxes, but we are especially interested in quick foxes:

quick^2 fox

The default boost value is 1, but can be any positive floating point number. Boosts between 0 and 1 reduce relevance.

Boosts can also be applied to phrases or to groups:

"john smith"^2   (foo bar)^4

Boolean operatorsedit

By default, all terms are optional, as long as one term matches. A search for foo bar baz will find any document that contains one or more of foo or bar or baz. We have already discussed thedefault_operator above which allows you to force all terms to be required, but there are also boolean operators which can be used in the query string itself to provide more control.

The preferred operators are + (this term must be present) and - (this term must not be present). All other terms are optional. For example, this query:

quick brown +fox -news

states that:

• fox must be present
• news must not be present
• quick and brown are optional — their presence increases the relevance

The familiar operators AND, OR and NOT (also written &&, || and !) are also supported. However, the effects of these operators can be more complicated than is obvious at first glance. NOT takes precedence over AND, which takes precedence over OR. While the + and - only affect the term to the right of the operator, AND and OR can affect the terms to the left and right.

Rewriting the above query using AND, OR and NOT demonstrates the complexity:

quick OR brown AND fox AND NOT news

This is incorrect, because  brown is now a required term.

(quick OR brown) AND fox AND NOT news

This is incorrect because at least one of  quick or  brown is now required and the search for those terms would be scored differently from the original query.

((quick AND fox) OR (brown AND fox) OR fox) AND NOT news

This form now replicates the logic from the original query correctly, but the relevance scoring bares little resemblance to the original.

In contrast, the same query rewritten using the match query would look like this:

{
    "bool": {
        "must":     { "match": "fox"         },
        "should":   { "match": "quick brown" },
        "must_not": { "match": "news"        }
    }
}

Groupingedit

Multiple terms or clauses can be grouped together with parentheses, to form sub-queries:

(quick OR brown) AND fox

Groups can be used to target a particular field, or to boost the result of a sub-query:

status:(active OR pending) title:(full text search)^2

Reserved charactersedit

If you need to use any of the characters which function as operators in your query itself (and not as operators), then you should escape them with a leading backslash. For instance, to search for (1+1)=2, you would need to write your query as \(1\+1\)\=2.

The reserved characters are: + - = && || > < ! ( ) { } [ ] ^ " ~ * ? : \ /

Failing to escape these special characters correctly could lead to a syntax error which prevents your query from running.

Watch this space

A space may also be a reserved character. For instance, if you have a synonym list which converts"wi fi" to "wifi", a query_string search for "wi fi" would fail. The query string parser would interpret your query as a search for "wi OR fi", while the token stored in your index is actually"wifi". Escaping the space will protect it from being touched by the query string parser: "wi\ fi".

Empty Queryedit

If the query string is empty or only contains whitespaces the query will yield an empty result set.