If neither OVERRIDING SYSTEM VALUE or OVERRIDING USER VALUE is specified:
If a value is not specified the database manager generates a new value.
For a Positioned UPDATE:
For more information, see update-clause.
A view column derived from the same column as another column of the view can be updated, but both columns cannot be updated in the same UPDATE statement.
If a list of column-names is specified, the number of expressions, NULLs, and DEFAULTS must match the number of column-names.
The number of expressions, NULLs, and DEFAULTs (or the number of result columns from a row-fullselect) must match the number of columns in the row.
For a Positioned UPDATE, if the UPDATE clause was specified in the SELECT statement of the cursor, each column of the table or view must also appear in the UPDATE clause. For more information, see update-clause.
ROW may not be specified for a view that contains a view column derived from the same column as another column of the view, because both columns cannot be updated in the same UPDATE statement.
A column-name in an expression must name a column of the named table or view. For each row updated, the value of the column in the expression is the value of the column in the row before the row is updated.
Each variable in the clause must identify a host structure or variable that is declared in accordance with the rules for declaring host structures and variables. In the operational form of the statement, a reference to a host structure is replaced by a reference to each of its variables. For further information on variables and structures, see References to host variables and Host structures. If a host structure is specified, the keyword ROW must be specified.
The row-fullselect may contain references to columns of the target table of the UPDATE statement. For each row updated, the value of such a column in the expression is the value of the column in the row before the row is updated.
The search-condition is applied to each row of the table or view. The updated rows are those for which the results of the search-condition are true.
If the search-condition contains a subquery, the subquery can be thought of as being executed each time the search-condition is applied to a row, and the results of that subquery used in applying the search-condition. In actuality, a subquery with no correlated references may be executed only once. A subquery with a correlated reference may have to be executed once for each row.
The table or view named must also be named in the FROM clause of the SELECT statement of the cursor, and the result table of the cursor must not be read-only. For an explanation of read-only result tables, see DECLARE CURSOR.
When the UPDATE statement is executed, the cursor must be positioned on a row; that row is updated.
Introduces the isolation level, which may be one of:
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