UPDATE

    UPDATE updates the current database file from another database file
    based on a one-to-one or one-to-many relation.

Syntax

    UPDATE ON <key exp> FROM <alias> REPLACE <field1> WITH <exp1>
    [,<field2> WITH <exp2>...] [RANDOM]

Arguments

    <key exp> is an expression used that defines matching records in the
    source work area.

    <alias> is the alias of the source work area used to update records in
    the current work area.

    <field1...fieldN> are the fields in the current work area to replace
    with new values.

    <exp1...expN> identifies the values to replace into the target fields.
    Fields from the source work area must be referenced with the alias of
    the respective work area.

Option

    Random: The RANDOM clause causes the entire source database file to
    be read allowing the source database file to be in any order.  If this
    option is specified, the target database file must be indexed on the
    <key exp>.

Usage

    UPDATE matches records in the target work area using the key expression
    as the argument of a lookup into the source work area.  To obtain an
    accurate UPDATE, both database files must be sorted or indexed on the
    key expression.  If the source database file is not sorted or indexed,
    use the RANDOM clause.

    Relations between work areas: UPDATE supports both one-to-one and
    one-to-many relations between the target and the source work areas.  It
    does not, however, support many-to-many or many-to-one relations.  All
    source records matching the <key exp> UPDATE only the first instance of
    the matching target records.

    Types of replacement: When you UPDATE, the REPLACE expression
    determines the type of UPDATE made to a target field.  If the UPDATE to
    the field adds to the target field, the formulation is:

    REPLACE <target field> WITH <target field> + <expN>

    Likewise, if the UPDATE subtracts from the target field, the
    formulation is:

    REPLACE <target field> WITH <target field> - <expN>

    Deleted records: When DELETED is ON, all target records are UPDATEd
    including deleted ones.  Deleted source records, however, are ignored.

Network

    In order to UPDATE in a network environment, the target database file
    must be locked with FLOCK() or USEd EXCLUSIVEly.  The source file may
    either be USEd EXCLUSIVEly or shared.