Knowledge Base - Technical Articles
FAQ: Why does the attribute table have Null or empty values after a join?
| Article ID: | 31122 |
|---|---|
| Software: | ArcGIS - ArcEditor 9.0, 9.1, 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcInfo 9.0, 9.1, 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcView 9.0, 9.1, 9.2, 9.3, 9.3.1, 10 |
| Platforms: | N/A |
Question
Why does the attribute table have Null or empty values after a join?
Answer
After performing a join between a feature class and a stand-alone table, such as dBASE IV, dBASE V, CSV, or PRN, the values in the fields from the joined table are empty or Null.
Null values can be the result of several factors:
-Values in the specified fields for the join do not match. Joins are also case sensitive. For example, 'NEW YORK' will not join with 'New York'. To convert string values to the proper case, please refer to the Technical Article in the Related Information section below.
-The name of the table or feature class, or field names in the table or feature class, include spaces or special characters.-show me-
-The table is stored in an Microsoft Access database that is not a personal geodatabase.-show me-
-The field names in the table are Microsoft Access reserved words. For a list of reserved words, see the Related Information section below.
Null values can be the result of several factors:
-Values in the specified fields for the join do not match. Joins are also case sensitive. For example, 'NEW YORK' will not join with 'New York'. To convert string values to the proper case, please refer to the Technical Article in the Related Information section below.
-The name of the table or feature class, or field names in the table or feature class, include spaces or special characters.
| Question |
What characters should not be used in ArcGIS for field names and table names? |
| Answer |
For ArcGIS to work with multiple data types, certain characters in field or table names are not supported. These characters include spaces, hyphens, such as in the term 'x-coord', brackets, and other special characters. These limits are imposed so that ArcGIS is able to function with the maximum amount of data types.
• Eliminate any characters that are not alphanumeric character or an underscore. • Do not start field or table names with an underscore or a number. • It is necessary to edit the field names in delimited text files to remove unsupported characters before using them. The limit for the length of field and table names depends on the underlying database management system (DBMS). Consult the DBMS documentation for information on naming limits for a particular DBMS. A dBASE field name can be up to 10 characters long, and there is no limit on the length of the table name. • For coverages, use up to 16 letters or numbers. Coverage items or field names must begin with a letter, and cannot contain spaces. |
-The table is stored in an Microsoft Access database that is not a personal geodatabase.
| Summary |
Neither adding a Microsoft Access table directly into ArcMap nor opening and modifying a Personal Geodatabase in Microsoft Access is supported by ESRI because this can damage the Access database. Instructions provided describe how to use Microsoft Access tables in ArcGIS by way of an OLE DB connection.
 Even though Microsoft Access Databases and ESRI's Personal Geodatabases are both built on the MDB file format, they should not be opened through their non-native software. |
| Procedure |
Use the following procedure to create an OLE DB connection to the Access Database:
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-The field names in the table are Microsoft Access reserved words. For a list of reserved words, see the Related Information section below.
Related Information
- What characters should not be used in ArcGIS for field names and table names?
For ArcGIS to work with multiple data types, certain characters in field or table names are not supported. These characters include spaces, hyphens, such as in the term 'x-coord', brackets, and other special characters. These limits are imposed so... - Use Microsoft Access tables in ArcGIS
Neither adding a Microsoft Access table directly into ArcMap nor opening and modifying a Personal Geodatabase in Microsoft Access is supported by ESRI because this can damage the Access database. Instructions provided describe how to use Microsoft... - Format a table in Microsoft Excel for use in ArcMap
Instructions provided explain how to format a table in Microsoft Excel for use in ArcMap. ArcMap does not read the native format for MS Excel (*.xls), but is able to read the following table formats: -dBase IV -dBase V -PRN -CSV Create... - Format a table in Microsoft Access for use in ArcMap
Instructions provided explain how to format a table in Microsoft Access for use in ArcMap. ArcMap is able to read the following table formats: -dBase IV -dBase V -PRN -CSV Create these files in Microsoft Excel or Microsoft Access. {N... - Convert a string to proper case in the ArcMap Field Calculator
{WARN}The procedure below is for ArcGIS 9.3.1 or earlier versions. Starting at ArcGIS 10.0, expressions in the Field Calculator are created using only VBScript or a standard Python format. {/WARN} Instructions provided describe how to use the Ar... - Microsoft Support - List of reserved words in Access 2002 and Access 2003
Created: 6/27/2006
Last Modified: 12/6/2011
By Anonymous - 01/09/2008 6:19 PM
Great article! It helped a lot!
This article saved me when I couldn't figure out why my join fields were all empty. Thanks!!! P.S. The rating scale is confusing... it looks like it goes from three stars to Good. Is Good the lowest rating?