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 are matched to the records in the Input Table parameter. 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, Feature Class To Feature Class, or Table To 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.
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.
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.
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
Add Join example: One-to-many join when each table has an Object ID field The second table uses a join table with no Object ID; only a one-to-first join is possible.
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
Add Join example: One-to-first join when either table does not have an Object ID field Last, 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.
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>
Add Join Example: One-to-many join when each table has an Object ID field and the Keep All Target Features parameter is checked The input table must have an Object ID field to perform a one-to-many join.
Records from the join table can be matched to more than one record if it 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 only matching records option, 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 saved by saving the ArcGIS Pro session or by saving it to a layer file using the Save Layer To File tool.
In the resulting input 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 the following fields: landuse.A, landuse.B, lookup_tab.C, and lookup_tab.D.
Indexing the fields in the input table and join table on which the join will be based can improve performance. Fields can be indexed with the Add Attribute Index 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 carried forward to 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, 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 this tool's 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.
Syntax
arcpy.management.AddJoin(in_layer_or_view, in_field, join_table, join_field, {join_type})| Parameter | 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.
| Boolean |
Derived Output
| Name | Explanation | Data Type |
| out_layer_or_view | The updated input dataset. | Table View; Raster Layer; Mosaic Layer |
Code sample
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.AddJoin_management("vegetation", "HOLLAND95",
"vegtable", "HOLLAND95")
arcpy.CopyFeatures_management(veg_joined_table, "vegjoin")This stand-alone script shows the AddJoin function as part of a workflow to join a table to a feature class and to extract desired 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.AddJoin_management(inFeatures, joinField, joinTable,
joinField)
# Select desired features from veg_layer
arcpy.SelectLayerByAttribute_management(veg_joined_table, "NEW_SELECTION",
expression)
# Copy the layer to a new permanent feature class
arcpy.CopyFeatures_management(veg_joined_table, outFeature)Environments
Licensing information
- Basic: Yes
- Standard: Yes
- Advanced: Yes