SQL-J Language Reference,
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FOR UPDATE clause

The FOR UPDATE clause is an optional part of a SELECT statement. The FOR UPDATE clause specifies whether the ResultSet of a simple SELECT statement that meets the requirements for a cursor is updatable or not. For more information about updatability, see “Requirements for Updatable Cursors”.

Syntax

FOR
{
    READ ONLY |
    UPDATE [ OF SimpleColumnName [ , SimpleColumnName]* ]
}

SimpleColumnName refers to the names visible for the table specified in the FROM clause of the underlying query.

Cursors are read-only by default. For a cursor to be updatable, you must specify FOR UPDATE.

To restrict the columns that are updatable through the cursor, you can specify a list of column names. For updatable cursors, the query optimizer avoids any index that includes an updatable column. Specifying a list of column names in the FOR UPDATE clause allows the optimizer to choose an index on any column not specified. For more information about how indexes affect cursors, see Tuning Cloudscape.

Example

SELECT hotel_id, booking_date, rooms_taken
FROM HotelAvailability
FOR UPDATE OF rooms_taken
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