[role="xpack"]
[[sql-functions-search]]
=== Full-Text Search Functions

Search functions should be used when performing full-text search, namely
when the `MATCH` or `QUERY` predicates are being used.
Outside a, so-called, search context, these functions will return default values
such as `0` or `NULL`.

{es-sql} optimizes all queries executed against {es} depending on the scoring needs.
Using <<_track_scores,`track_scores`>> on the search request or <<sort-search-results,`_doc` sorting>> that
disables scores calculation, {es-sql} instructs {es} not to compute scores when these are not needed.
For example, every time a `SCORE()` function is encountered in the SQL query, the scores are computed.

[[sql-functions-search-match]]
==== `MATCH`

.Synopsis:
[source, sql]
--------------------------------------------------
MATCH(
    field_exp,   <1>
    constant_exp <2>
    [, options]) <3>
--------------------------------------------------

*Input*:

<1> field(s) to match
<2> matching text
<3> additional parameters; optional

*Description*: A full-text search option, in the form of a predicate, available in {es-sql} that gives the user control over powerful <<query-dsl-match-query,match>>
and <<query-dsl-multi-match-query,multi_match>> {es} queries.

The first parameter is the field or fields to match against. In case it receives one value only, {es-sql} will use a `match` query to perform the search:

[source, sql]
----
include-tagged::{sql-specs}/docs/docs.csv-spec[simpleMatch]
----

However, it can also receive a list of fields and their corresponding optional `boost` value. In this case, {es-sql} will use a
`multi_match` query to match the documents:

[source, sql]
----
include-tagged::{sql-specs}/docs/docs.csv-spec[multiFieldsMatch]
----

NOTE: The `multi_match` query in {es} has the option of <<query-dsl-multi-match-query,per-field boosting>> that gives preferential weight
(in terms of scoring) to fields being searched in, using the `^` character. In the example above, the `name` field has a greater weight in
the final score than the `author` field when searching for `frank dune` text in both of them.

Both options above can be used in combination with the optional third parameter of the `MATCH()` predicate, where one can specify
additional configuration parameters (separated by semicolon `;`) for either `match` or `multi_match` queries. For example:

[source, sql]
----
include-tagged::{sql-specs}/docs/docs.csv-spec[optionalParamsForMatch]
----

NOTE: The allowed optional parameters for a single-field `MATCH()` variant (for the `match` {es} query) are: `analyzer`, `auto_generate_synonyms_phrase_query`,
`lenient`, `fuzziness`, `fuzzy_transpositions`, `fuzzy_rewrite`, `minimum_should_match`, `operator`,
`max_expansions`, `prefix_length`.

NOTE: The allowed optional parameters for a multi-field `MATCH()` variant (for the `multi_match` {es} query) are: `analyzer`, `auto_generate_synonyms_phrase_query`,
`lenient`, `fuzziness`, `fuzzy_transpositions`, `fuzzy_rewrite`, `minimum_should_match`, `operator`,
`max_expansions`, `prefix_length`, `slop`, `tie_breaker`, `type`.


[[sql-functions-search-query]]
==== `QUERY`

.Synopsis:
[source, sql]
--------------------------------------------------
QUERY(
    constant_exp <1>
    [, options]) <2>
--------------------------------------------------

*Input*:

<1> query text
<2> additional parameters; optional

*Description*: Just like `MATCH`, `QUERY` is a full-text search predicate that gives the user control over the <<query-dsl-query-string-query,query_string>> query in {es}.

The first parameter is basically the input that will be passed as is to the `query_string` query, which means that anything that `query_string`
accepts in its `query` field can be used here as well:

[source, sql]
----
include-tagged::{sql-specs}/docs/docs.csv-spec[simpleQueryQuery]
----

A more advanced example, showing more of the features that `query_string` supports, of course possible with {es-sql}:

[source, sql]
----
include-tagged::{sql-specs}/docs/docs.csv-spec[advancedQueryQuery]
----

The query above uses the `_exists_` query to select documents that have values in the `author` field, a range query for `page_count` and
regex and fuzziness queries for the `name` field.

If one needs to customize various configuration options that `query_string` exposes, this can be done using the second _optional_ parameter.
Multiple settings can be specified separated by a semicolon `;`:

[source, sql]
----
include-tagged::{sql-specs}/docs/docs.csv-spec[optionalParameterQuery]
----

NOTE: The allowed optional parameters for `QUERY()` are: `allow_leading_wildcard`, `analyze_wildcard`, `analyzer`,
`auto_generate_synonyms_phrase_query`, `default_field`, `default_operator`, `enable_position_increments`,
`escape`, `fuzziness`, `fuzzy_max_expansions`, `fuzzy_prefix_length`, `fuzzy_rewrite`, `fuzzy_transpositions`,
`lenient`, `max_determinized_states`, `minimum_should_match`, `phrase_slop`, `rewrite`, `quote_analyzer`,
`quote_field_suffix`, `tie_breaker`, `time_zone`, `type`.


[[sql-functions-search-score]]
==== `SCORE`

.Synopsis:
[source, sql]
--------------------------------------------------
SCORE()
--------------------------------------------------

*Input*: _none_

*Output*: `double` numeric value

*Description*: Returns the {defguide}/relevance-intro.html[relevance] of a given input to the executed query. 
The higher score, the more relevant the data.

NOTE: When doing multiple text queries in the `WHERE` clause then, their scores will be
combined using the same rules as {es}'s
<<query-dsl-bool-query,bool query>>. 

Typically `SCORE` is used for ordering the results of a query based on their relevance:

[source, sql]
----
include-tagged::{sql-specs}/docs/docs.csv-spec[orderByScore]
----

However, it is perfectly fine to return the score without sorting by it:

[source, sql]
----
include-tagged::{sql-specs}/docs/docs.csv-spec[scoreWithMatch]
----
