Add Join (Data Management)—ArcGIS AllSource

Summary

Joins a layer to another layer or table based on a common field. Feature layers, table views, and raster layers with a raster attribute table are supported.

The records in the Join Table parameter value will be matched to the records in the Input Table parameter value. A match is made when the input join field and join table field values are equal. This join is temporary.

Illustration

Usage

The Input Table parameter value can be a feature layer, a table view, or a raster layer with an attribute table. If a data path is used, the layer will be created with the join. The join will always reside in the layer, not with the data.
To make a permanent join, either use the Join Field tool or use the joined layer as input to one of the following tools: Copy Features, Copy Rows, Export Features, or Export Table. When saving the results to a new feature class or table, the Qualified Field Names environment can be used to control whether the joined output field names will be qualified with the name of the table the field came from. Field aliases are persisted from the layer to the output, except when the output is a shapefile.
If the input is a feature class or dataset path, this tool will automatically create and return a new layer with the result of the tool applied.
When a one-to-many join is produced by the join, the result of the join can be viewed in the attribute table, where a warning message will indicate if the table has duplicate Object IDs. Because many geoprocessing tools do not support data with duplicate Object IDs and processing such data can produce unexpected results, it is recommended that you first copy the joined layer to a new feature class using the Export Features tool. Then use the new feature class as input to other geoprocessing tools.

The following tables include possible outcomes of performing a join with various inputs.

The first table shows a one-to-many join. Keeping only matching records will not have any affect, as all records have matches.

Add Join example: One-to-many join when each table has an Object ID field
Input table		Join table		Result
Input field	Type	Join field	Value	Input field	Type	Join field	Value
1	A	1	100	1	A	1	100
2	B	2	200	2	B	2	200
		1	300	1	A	1	300
		2	400	2	B	2	400

The second table uses a join table with no Object ID; only a one-to-first join is possible. A one-to-first join is also only possible if each table is from a different workspace.

Add Join example: One-to-first join when either table does not have an Object ID field
Input table		Join table		Result
Input field	Type	Join field	Value	Input field	Type	Join field	Value
1	A	1	100	1	A	1	100
2	B	2	200	2	B	2	200
		3	300
		4	400

In the last table, the input table has more records than the join table; keeping all records will keep all of the matching records plus the records from the input table that did not match.

Add Join Example: One-to-many join when each table has an Object ID field and the Keep All Target Features parameter is checked
Input table		Join table		Result
Input field	Type	Join field	Value	Input field	Type	Join field	Value
1	A	1	100	1	A	1	100
2	B	2	200	2	B	2	200
3	C	1	300	1	A	1	300
4	D	2	400	2	B	2	400
				3	C	<Null>	<Null>
				4	D	<Null>	<Null>

The input table must have an Object ID field to perform a one-to-many join and be in the same workspace.

Records from the join table can be matched to more than one record if the join table has an Object ID field; otherwise, a one-to-first join will be performed.
When joining tables, the default option is to keep all records. If a record in the target table doesn't have a match in the join table, that record is given null values for all the fields being appended into the target table from the join table.
Input table Join table Result
Input field
Type
Join field
Value
Input field
Type
Join field
Value
1
A
1
100
1
A
1
100
2
B
2
200
2
B
2
200
3
C
1
300
1
A
1
300
4
D
2
400
2
B
2
400
3
C
<Null>
<Null>
4
D
<Null>
<Null>
With the Keep All Target Features parameter, if a record in the target table doesn't have a match in the join table, that record is removed from the resultant target table. If the target table is the attribute table of a layer, features that don't have data joined to them are not shown on the map.
Input table Join table Result
Input field
Type
Join field
Value
Input field
Type
Join field
Value
1
A
1
100
1
A
1
100
2
B
2
200
2
B
2
200
3
300
4
400
Field properties, such as aliases, visibility, and number formatting, are maintained when a join is added or removed.
An input table is allowed one join at a time.
The join persists only for the duration of the layer. A layer can be retained by saving the AllSource session or by saving it to a layer file using the Save Layer To File tool.

To see the results of a join created in a script tool, the tool must include the layer as a derived output parameter. Similarly, the Updated Input Layer or Table View parameter must be set as a derived output parameter in a model tool to see the joined results.
In the resulting table, fields will be prefixed with the input's name and a period (.), and all fields from the join table will be prefixed with the join table name and a period as the default.
For example, joining landuse, which has fields A and B, to lookup_tab, which has fields C and D, will result in a layer or table view with landuse.A, landuse.B, lookup_tab.C, and lookup_tab.D fields.
A layer must have unique field names. If both the input and joined tables have the same name and are in different workspaces, a join cannot be preformed without creating a poorly defined layer.
Indexing the fields in the input table and join table on which the join will be based can improve performance. If the Index Joined Fields parameter is checked, an attribute index will be added to both joining fields. Alternatively, each joining field can be indexed with the Add Attribute Index tool.
If the join results are unexpected or incomplete, review whether the Join Table Field and Input Join Field parameter values are indexed. If they're not, try deleting and re-creating the index and rerun the tool.
If the input layer or table view's fields were modified (renamed or hidden) using the Field Info parameter in the Make Feature Layer or Make Table View tool, the field modifications will not be included in the output joined layer or table view.
The definition query of the join table will be applied to the input layer or table view. The definition query can be removed using the Remove Join tool or by manually removing the definition query from the layer.
The Validate Join tool can be used to validate a join between two layers or tables to determine if the layers or tables have valid field names and Object ID fields, if the join produces matching records, if the join is a one-to-one or one-to-many join, and other properties of the join.
A button to validate the join is available on the tool dialog box for ease of use.
Any selections on the layer are not used in the Add Join tool but are used in the Join Field tool.

Parameters

Label	Explanation	Data Type
Input Table	The layer or table view to which the join table will be joined.	Mosaic Layer; Raster Layer; Table View
Input Join Field	The field in the input layer or table view on which the join will be based.	Field
Join Table	The table or table view to be joined to the input layer or table view.	Mosaic Layer; Raster Layer; Table View
Join Table Field	The field in the join table that contains the values on which the join will be based.	Field
Keep All Target Features (Optional)	Specifies whether only records in the input that match a record in the join table will be included in the output. Checked—All records in the input layer or table view will be included in the output. This is also known as an outer join. This is the default. Unchecked—Only those records in the input that match a row in the join table will be included in the output. This is also known as an inner join.	Boolean
Index Joined Fields (Optional)	Specifies whether table attribute indexes will be added to both joining fields. Checked—Both join fields will be indexed. If the table has an existing index, a new index will not be added. Unchecked—Indexes will not be added. This is the default.	Boolean

Derived Output

Label	Explanation	Data Type
Updated Input Layer or Table View	The updated input dataset.	Table View; Raster Layer; Mosaic Layer

arcpy.management.AddJoin(in_layer_or_view, in_field, join_table, join_field, {join_type}, {index_join_fields})

Name	Explanation	Data Type
in_layer_or_view	The layer or table view to which the join table will be joined.	Mosaic Layer; Raster Layer; Table View
in_field	The field in the input layer or table view on which the join will be based.	Field
join_table	The table or table view to be joined to the input layer or table view.	Mosaic Layer; Raster Layer; Table View
join_field	The field in the join table that contains the values on which the join will be based.	Field
join_type (Optional)	Specifies whether only records in the input that match a record in the join table will be included in the output. KEEP_ALL—All records in the input layer or table view will be included in the output. This is also known as an outer join. This is the default. KEEP_COMMON—Only those records in the input that match a row in the join table will be included in the output. This is also known as an inner join.	Boolean
index_join_fields (Optional)	Specifies whether table attribute indexes will be added to both joining fields. INDEX_JOIN_FIELDS—Both join fields will be indexed. If the table has an existing index, a new index will not be added. NO_INDEX_JOIN_FIELDS—Indexes will not be added. This is the default.	Boolean

Derived Output

Name	Explanation	Data Type
out_layer_or_view	The updated input dataset.	Table View; Raster Layer; Mosaic Layer

Code sample

AddJoin example 1 (Python window)

The following Python window script demonstrates how to use the AddJoin function in immediate mode.

import arcpy
arcpy.env.workspace = "C:/data/Habitat_Analysis.gdb"
veg_joined_table = arcpy.management.AddJoin("vegetation", "HOLLAND95", 
                                            "vegtable", "HOLLAND95")
arcpy.management.CopyFeatures(veg_joined_table, "vegjoin")

AddJoin example 2 (stand-alone script)

This stand-alone script shows the AddJoin function as part of a workflow to join a table to a feature class and to extract specified features.

# Name: AttributeSelection.py
# Purpose: Join a table to a featureclass and select the desired attributes

# Import system modules
import arcpy

# Set environment settings
arcpy.env.workspace = "C:/data/Habitat_Analysis.gdb"
# The qualifiedFieldNames environment is used by Copy Features when persisting 
# the join field names.
arcpy.env.qualifiedFieldNames = False

# Set local variables
inFeatures = "vegtype"
joinTable = "vegtable"
joinField = "HOLLAND95"
expression = "vegtable.HABITAT = 1"
outFeature = "vegjoin"

# Join the feature layer to a table
veg_joined_table = arcpy.management.AddJoin(inFeatures, joinField, joinTable, 
                                            joinField)

# Select desired features from veg_layer
arcpy.management.SelectLayerByAttribute(veg_joined_table, "NEW_SELECTION", 
                                        expression)

# Copy the layer to a new permanent feature class
result = arcpy.management.CopyFeatures(veg_joined_table, outFeature)

# See field names and aliases
resultFields = arcpy.ListFields(result)
print([field.name for field in resultFields])
print([field.aliasName for field in resultFields])

Environments

Current Workspace

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Summary

Illustration

Usage

Parameters

Derived Output

Derived Output

Code sample

Environments

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