join
Description
You can use the join
command to combine the results of a main search (left-side dataset) with the results of either another dataset or a subsearch (right-side dataset). You can also combine a search result set to itself using the selfjoin
command.
The left-side dataset is the set of results from a search that is piped into the join
command and then merged on the right side with the either a dataset or the results from a subsearch. The left-side dataset is sometimes referred to as the source data.
The following search example joins the source data from the search pipeline with a subsearch on the right side. Rows from each dataset are merged into a single row if the where
predicate is satisfied.
<left-dataset> | join left=L right=R where L.pid = R.pid [subsearch]
A maximum of 50,000 rows in the right-side dataset can be joined with the left-side dataset. This maximum default is set to limit the impact of the join
command on performance and resource consumption.
If you are familiar with SQL but new to SPL, see Splunk SPL for SQL users.
Alternative commands
For flexibility and performance, consider using one of the following commands if you do not require join semantics. These commands provide event grouping and correlations using time and geographic location, transactions, subsearches, field lookups, and joins.
Command | Use |
---|---|
append |
To append the results of a subsearch to the results of your current search. The events from both result sets are retained.
|
appendcols |
Appends the fields of the subsearch results with the input search result fields. The first subsearch result is merged with the first main result, the second subsearch result is merged with the second main result, and so on. |
lookup |
Use when one of the result sets or source files remains static or rarely changes. For example, a file from an external system such as a CSV file.
The lookup cannot be a subsearch. |
search |
In the most simple scenarios, you might need to search only for sources using the OR operator and then use a stats or transaction command to perform the grouping operation on the events.
|
stats |
To group events by a field and perform a statistical function on the events. For example to determine the average duration of events by host name.
|
transaction
|
Use transaction in the following situations.
|
For information about when to use a join, see the flowchart in About event grouping and correlation in the Search Manual.
Syntax
The required syntax is in bold.
- join
- [<join-options>...]
- [<field-list>] | [left=<left-alias>] [right=<right-alias>] where <left-alias>.<field>=<right-alias>.<field> [<left-alias>.<field>=<right-alias>.<field>]...
- <dataset-type>:<dataset-name> | <subsearch>
Required arguments
- dataset-type
- Syntax: datamodel | savedsearch | inputlookup
- Description: The type of dataset that you want to use to join with the source data. The dataset must be a dataset that you created or are authorized to use. You can specify
datamodel
,savedsearch
, orinputlookup
. The dataset type must precede the dataset name. For example,savedsearch:<dataset-name>
.
- You can use either
<dataset-type>:<dataset-name>
or<subsearch>
with thejoin
command, but not both.
- dataset-name
- Syntax: <dataset-name>
- Description: The name of the dataset that you want to use to join with the source data. The dataset must be a dataset that you created or are authorized to use. The dataset name must follow the dataset type. For example, if the dataset name is
january
and the dataset type is datamodel, you specifydatamodel:january
.
- You can use either
<dataset-type>:<dataset-name>
or<subsearch>
with thejoin
command, but not both.
- subsearch
- Syntax: [<subsearch>]
- Description: A secondary search or dataset that specifies the source of the events that you want to join to. The subsearch must be enclosed in square brackets. The results of the subsearch should not exceed available memory.
- You can use either
<dataset-type>:<dataset-name>
or<subsearch>
in a search, but not both. When[<subsearch>]
is used in a search by itself with no join keys, the Splunk software autodetects common fields and combines the search results before thejoin
command with the results of the subsearch.
Optional arguments
- join-options
- Syntax: type=(inner | outer | left) | usetime=<bool> | earlier=<bool> | overwrite=<bool> | max=<int>
- Description: Arguments to the join command. Use either
outer
orleft
to specify a left outer join. See Descriptions for the join-options argument in this topic.
- field-list
- Syntax: <field> <field> ...
- Description: Specify the list of fields to use for the join. For example, to join fields
ProductA
,ProductB
, andProductC
, you would specify| join ProductA ProductB ProductC...
. If<field-list>
is specified, one or more of the fields must be common to each dataset. If no fields are specified, all of the fields that are common to both datasets are used.
- left alias
- Syntax: left=<left-alias>
- Description: The alias to use with the left-side dataset, the source data, to avoid naming collisions. Must be combined with the right alias and
where
clause, or the alias is ignored.
- The left alias must be used together with the right alias.
- right alias
- Syntax: right=<right-alias>
- Description: The alias to use with the right-side dataset to avoid naming collisions. Must be combined with the left alias and the
where
clause, or the alias is ignored.
- The right alias must be used together with the left alias.
- where clause
- Syntax: where <left-alias>.<field>=<right-alias>.<field>...
- Description: Identifies the names of the fields in the left-side dataset and the right-side dataset that you want to join on. You must specify the left and right aliases and the field name. Fields that are joined from the left and right datasets do not have to have the same names. For example:
where L.host=R.user
matches events in thehost
field from the left dataset with events in theuser
field from the right dataset.
- The
where
clause must be used with the right and left aliases and field name.
- You can specify the aliases and fields in a
where
clause on either side of the equal sign. For example:
where <left-alias>.<left-field>=<right-alias>.<right-field>
- or
where <right-alias>.<right-field>=<left-alias>.<left-field>
Descriptions for the join-options argument
- type
- Syntax: type=inner | outer | left
- Description: Indicates the type of join to perform. The difference between an
inner
and aleft
(orouter
) join is how the events are treated in the main search that do not match any of the events in the subsearch. In both inner and left joins, events that match are joined. The results of aninner
join do not include events from the main search that have no matches in the subsearch. The results of aleft
(orouter
) join includes all of the events in the main search and only those values in the subsearch have matching field values. - Default:
inner
- usetime
- Syntax: usetime=<bool>
- Description: A Boolean value that Indicates whether to use time to limit the matches in the subsearch results. Used with the
earlier
option to limit the subsearch results to matches that are earlier or later than the main search results. - Default:
false
- earlier
- Syntax: earlier=<bool>
- Description: If
usetime=true
andearlier=true
, the main search results are matched only against earlier results from the subsearch. Ifearlier=false
, the main search results are matched only against later results from the subsearch. Results that occur at the same time (second) are not eliminated by either value. - Default:
true
- overwrite
- Syntax: overwrite=<bool>
- Description: If fields in the main search results and subsearch results have the same name, indicates whether fields from the subsearch results overwrite the fields from the main search results.
- Default:
true
- max
- Syntax: max=<int>
- Description: Specifies the maximum number of subsearch results that each main search result can join with. If set to
max=0
, there is no limit. - Default:
1
Usage
The join
command is a centralized streaming command when there is a defined set of fields to join to. Otherwise the command is a dataset processing command.
See Command types.
A subsearch can be initiated through a search command such as the join
command. See Initiating subsearches with search commands in the Splunk Cloud Platform Search Manual.
Limitations on subsearches in joins
Use the join
command when the results of the subsearch are relatively small, for example 50,000 rows or less. To minimize the impact of this command on performance and resource consumption, Splunk software imposes some default limitations on the subsearch.
Limitations on the subsearch for the join
command are specified in the limits.conf
file. The limitations include a maximum of 50,000 rows in the subsearch to join against and the maximum search time for the subsearch. See Subsearches in the Search Manual.
- Splunk Cloud Platform
- To change the
join
command subsearch limitations, request help from Splunk Support. If you have a support contract, file a new case using the Splunk Support Portal at Support and Services. Otherwise, contact Splunk Customer Support.
- Splunk Enterprise
- To change the
subsearch_maxout
orsubsearch_maxtime
settings in your limits.conf file forjoin
command subsearches, follow these steps.
- Prerequisites
- Only users with file system access, such as system administrators, can edit configuration files.
- Review the steps in How to edit a configuration file in the Splunk Enterprise Admin Manual.
Never change or copy the configuration files in the default directory. The files in the default directory must remain intact and in their original location. Make changes to the files in the local directory.
- Steps:
- Open or create a local limits.conf file at $SPLUNK_HOME/etc/system/local.
- Under the
[join]
stanza, add the linesubsearch_maxout = <value>
orsubsearch_maxtime = <value>
.
One-to-many and many-to-many relationships
To return matches for one-to-many, many-to-one, or many-to-many relationships, include the max
argument in your join
syntax and set the value to 0. By default max=1
, which means that the subsearch returns only the first result from the subsearch. Setting the value to a higher number or to 0, which is unlimited, returns multiple results from the subsearch.
Basic examples
1. A basic join
Combine the results from a main search with the results from a subsearch search vendors
. The result sets are joined on the product_id
field, which is common to both sources.
... | join product_id [search vendors]
2. Returning all subsearch rows
By default, only the first row of the subsearch that matches a row of the main search is returned. To return all of the matching subsearch rows, include the max=<int>
argument and set the value to 0. This argument joins each matching subsearch row with the corresponding main search row.
... | join product_id max=0 [search vendors]
3. Join datasets on fields that have the same name
Combine the results from a search with the vendors
dataset. The data is joined on the product_id
field, which is common to both datasets.
... | join left=L right=R where L.product_id=R.product_id [search vendors]
4. Join datasets on fields that have different names
Combine the results from a search with the vendors
dataset. The data is joined on a product ID field, which have different field names in each dataset. The field in the left-side dataset is product_id
. The field in the right-side dataset is pid
.
... | join left=L right=R where L.product_id=R.pid [search vendors]
4. Use words instead of letters as aliases
You can use words for the aliases to help identify the datasets involved in the join. This example uses products
and vendors
for the aliases.
... | join left=products right=vendors where products.product_id=vendors.pid [search vendors]
Extended examples
1. Specifying dataset aliases with a saved search dataset
This example joins each matching right-side dataset row with the corresponding source data row. This example uses products
, which is a savedsearch type of dataset, for the right-side dataset. The field names in the left-side dataset and the right-side dataset are different. This search returns all of the matching rows in the left and right datasets by including max=0
in the search.
... | join max=0 left=L right=R where L.vendor_id=R.vid savedsearch:products
2. Use aliasing with commands following the join
Commands following the join can take advantage of the aliasing provided through the join
command. For example, you can use the aliasing in another command like stats
as shown in the following example.
... | join left=L right=R where L.product_id=R.pid [search vendors] | stats count by L.product_id
3. Using a join to display resource usage information
The dashboards and alerts in the distributed management console shows you performance information about your Splunk deployment. The Resource Usage: Instance dashboard contains a table that shows the machine, number of cores, physical memory capacity, operating system, and CPU architecture.
To display the information in the table, use the following search. This search includes the join
command. The search uses the information in the dmc_assets table to look up the instance name and machine name. The search then uses the serverName
field to join the information with information from the /services/server/info
REST endpoint. The /services/server/info
is the URI path to the Splunk REST API endpoint that provides hardware and operating system information for the machine. The $splunk_server$
part of the search is a dashboard token variable.
| inputlookup dmc_assets | search serverName = $splunk_server$ | stats first(serverName) AS serverName, first(host) AS host, first(machine) AS machine | join type=left serverName [ | rest splunk_server=$splunk_server$ /services/server/info | fields serverName, numberOfCores, physicalMemoryMB, os_name, cpu_arch] | fields machine numberOfCores physicalMemoryMB os_name cpu_arch | rename machine AS Machine, numberOfCores AS "Number of Cores", physicalMemoryMB AS "Physical Memory Capacity (MB)", os_name AS "Operating System", cpu_arch AS "CPU Architecture"
See also
iplocation | kmeans |
This documentation applies to the following versions of Splunk Cloud Platform™: 8.2.2202, 8.2.2112, 8.2.2201
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