問題文
A report builds a display name by joining a first name, a middle name and a last name with the concatenation operator. Some rows hold a null middle name. What does the expression return for those rows?
選択肢
- It returns a null for the whole expression, because every operator that receives a null operand hands back a null as its result.
- It returns the remaining operands joined with one space between them, because the operator inserts a separator where a null operand sits.
- It returns the remaining operands joined together, because concatenation is the one operator that reads a null operand as text of zero length.
- It returns an error while the row is fetched, because the operator checks that each operand holds a value before it joins them.