DELETE 和 INSERT 语句不支持集合派生表段的 row 变量。
EXEC SQL BEGIN DECLARE SECTION;
row(x int, y int, length float, width float) a_row;
EXEC SQL END DECLARE SECTION;
EXEC SQL update table(:a_row)
set x=0, y=0, length=10, width=20;
EXEC SQL update rectangles set rect = :a_row;