@DbColumn (ODBC data source) (Formula Language)

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.

cache

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 Domino® retrieves the latest information for every lookup, specify this option.

data_source

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."

user_ID1 : user_ID2

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."

password1 : password2

Text list. The passwords required by the user IDs.

See "Specifying IDs and passwords."

table

Text. The name of the database table being accessed.

column

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

null_handling

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

See "Specifying null handling."

"Distinct"

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

See "Specifying Distinct."

sort

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."

Return value

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.

Note: If you use the option button or the check box user interface for a keywords field, Domino® updates the keyword list only when the document is composed or is loaded for editing. If you use the Standard user interface for the list, the keyword list is updated every time the document is recalculated.

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

Specifying the table name

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 as described next).

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 Domino®.

Specifying Distinct

The Distinct string argument is similar to @Unique in 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 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 Domino®.

Note: Distinct is not supported by all ODBC drivers. If there are null values in the data and you specify Distinct, one null is usually returned.

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.

If no sort string argument is specified, values are returned in arbitrary 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

If the user's NOTES.INI file includes the statement

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 hard-coding 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.

Examples

This formula retrieves from the inventory database the complete list of colors in which your company's uniforms are available. The data is stored like this:

Item

Size

Color

Shirt

Small

Red

Skirt

Small

Green

Sweater

Medium

Red

Trousers

Medium

Yellow

Use @DbColumn to retrieve the entire contents of the Color column (column 3):
```
@DbColumn("ODBC";"INVENTORY";"";"";"UNIFORMS";"Color")
```
Values in the resulting list appear just as they were encountered in the database; they are not sorted and duplicate values are retained:
```
Red:Green:Red:Yellow
```
This example uses the sample "pubs" database that is included with Microsoft™ SQL Server. The formula uses the ODBC SQL Server driver to access the database, locate the table called "authors" that is owned by user "dbo," and then retrieve the list of names in the "au_lname" column. The author names are sorted in ascending order; null values are discarded.
```
@DbColumn("ODBC";"PUBLISHERS";"dbo";"vanilla";
"dbo.authors"; "au_lname":"Discard";"Ascending")
```

Item	Size	Color
Shirt	Small	Red
Skirt	Small	Green
Sweater	Medium	Red
Trousers	Medium	Yellow