Uses data source information to activate the appropriate ODBC driver. The driver then locates the specified DBMS, table, and column, and returns all values in that column. You can optionally specify whether the returned list of values is sorted, whether duplicate values are deleted, and how null values are handled.

Note @DbColumn can only retrieve data; it can't add, delete, or modify data.

Syntax

@DbColumn( "ODBC" : cache ; data_source ; user_ID1 : user_ID2 ; password1 : password2 ; table ; column : null_handling ; "Distinct" : sort )

Parameters

"ODBC"

String argument. Indicates that you are accessing an ODBC data source.

String argument. Optional. In the initial lookup, specify either "" or "NoCache." If the former case, subsequent lookups to the same data source, you can specify "ReCache."
• "" (null string) caches the results of the lookup. Each subsequent lookup to the same location (within the same Domino session and so long as the database executing this lookup remains open) reuses that data until you specify "ReCache." Cached data improves performance and may be a good choice for stable data.
• "ReCache" refreshes the cache with the latest data from the database. If you want to ensure that this lookup gets the latest information, specify this option.
Note "ReCache" is new with Release 6.
• "NoCache" gets the results of the lookup from the database; no cache is used. If you want to ensure that Lotus Domino retrieves the latest information for every lookup, specify this option.

Text. The name of the external data source being accessed. A data source indicates the location of one or more database tables.

See "Specifying the data source."

Text list. The user IDs needed to connect to the external database. You may need up to two IDs, depending on the DBMS being accessed.

See "Specifying IDs and passwords."

Text list. The passwords required by the user IDs.

See "Specifying IDs and passwords."

Text. The name of the database table being accessed.

Text. The name of the column from which data is being retrieved.

Text. Specifies how null values are treated when the data is retrieved.

See "Specifying null handling."

String argument. Optional. Removes duplicate values from the list before returning data.

See "Specifying Distinct."

String argument. Specify "Ascending" to sort the list of values into ascending order before it is returned; specify "Descending" to sort the list in descending order.

See "Specifying sort."

valuesFound

Text, number, date-time, or a list of these types. The values found in the column you indicated.

See "Accessing the values found," later in this chapter.

Specifying the data source

The data source name can contain up to 32 alphanumeric characters.

@DbLookup can access data sources that have already been registered in the ODBC.INI file (or similar registry on platforms other than Windows™).

Specifying IDs and passwords

You only need these arguments if your DBMS requires them.

Instead of storing the IDs in the @DbColumn formula, you can replace them with null strings (""). If an ID is required, the user will be prompted for it. This is useful when you do not want other designers to see IDs, or when you want users to enter their own IDs when accessing external data. However, you must include IDs and passwords in formulas that run automatically (such as an agent) because these formulas don't prompt for information.

The user IDs and passwords for accessing a data source are required only once per Domino database session, as long as that database remains open. If the user opens another Domino database and executes a formula that accesses the same data source, the user ID and password will be required again.

Password parameters are necessary only when ID parameters are specified. Like IDs, passwords can either be stored in the @DbColumn formula, or prompted for by substituting the null string. If the database password is null, you can omit it from the formula.

For example, for the full ID/password specification, enter:

• "";"" (two null strings, separated by a semicolon) to specify no ID and password, or to prompt for both
• "user_ID1";"password1" to specify one user ID and password combination
• "user_ID1":"user_ID2";"password1":"password2" to specify two user ID and password combinations

You can optionally include the name of the table's owner to remove ambiguity; use the format "owner_name.table_name", with a period to separate the owner name from the table name. For example:

"dbo.author"

Table can also refer to a database view in the DBMS being accessed.

Specifying null handling

Normally, null values are ignored and the resulting list is shortened (same as using the Discard option described below).

To control how null values are handled, specify one of the following, appended to the column parameter with a colon:

• "Fail" generates this error message if the column of data contains any null values:

  Null values found - canceling @Db function

  No data is returned with the message.

• "Discard" discards the null values, thus shortening the returned list of values. If one or more values are discarded when the @DbColumn formula is executed, you see this message on the status bar:

  Caution: NULL values discarded from @Db list.

• "Replacement value" specifies a replacement value for null values. The replacement value must be a quoted string, but if the column is numeric or date-time, the string must be convertible to that type.

  If your formula includes a sort string argument, the list of values to be returned is sorted before the replacement values are inserted. During sorting, all null values are placed at the beginning of the list for an ascending sort; and at the end for a descending sort. They are not replaced until sorting is complete. This can result in a list that has some values sorted incorrectly. For example, if you specify "zzz" as your replacement value, all the "zzz" values will appear at the beginning of the list, even if you sorted it in ascending order.

  If one or more values are replaced when the @DbColumn formula is executed, you see this message on the status bar:

  Caution: NULL value replaced with user-defined value in @Db list

  Generally, the replacement value should be one that is not likely to appear in the list as valid data; for example, if the column is text, your replacement value might be "***" so that you can easily find those values in Lotus Domino.

The Distinct string argument is similar to @Unique in Lotus Domino, except that Distinct ensures that duplicate values are removed before the data is returned. Using Distinct instead of @Unique has two advantages:

• The formula operates more quickly because the additional work is performed outside of Lotus Domino.
• You can potentially retrieve a larger amount of useful data into Domino -- since the duplicate values are removed at the back-end, more unique values can be returned to Lotus Domino.

Specifying sort

If you use the Distinct string argument, you can append the sort parameter to it with a colon. Use one of these keywords for the sort parameter to specify sorting of the return values:

• Ascending sorts the list in ascending order.
• Descending sorts the list in descending order.

Note The sort keywords are not supported by all ODBC drivers. If you attempt to use both Ascending and Descending in your formula, you see an "Invalid argument" message.

If multiple values are returned, they are formatted as a list and are separated with the multi-value separator designated for the current field.

@DbColumn can return no more than 64KB of data. Use the following equations to determine how much of your data can be returned with @DbColumn.

• For lookups that return text:

  2 + (2 * number of entries returned) + total text size of all entries

  Each text string is limited to 511 bytes; if only one text string is returned, it is limited to 64KB.

• For lookups that return numbers or dates:

  (10 * number of entries returned) + 6

NoExternalApps=1

the @DbColumn formula is disabled. The user will not see an error message; the formula fails to execute. This applies to @DbColumn only when you use it with ODBC.

Usage

@DbColumn is intended mainly for keyword formulas. Instead of hard­coding a list of keywords and then periodically updating that list, @DbColumn allows you to dynamically retrieve a list of values from an external database table.

This function only works in Web applications if the remote server hosting the table from which data is being retrieved exists on the same machine as the Domino server, which is rarely the case.

Language cross-reference

GetValue method of Lotus Connectors ODBCResultSet class

Example
See Also

Accessing external databases through LS:DO using @functions
@DbColumn (Domino data source)
@DbCommand (ODBC data source)
@DbLookup (ODBC data source)
@Functions with ECL security

Glossary