单项选择题 Given the following requirements: Create a table to contain employee data, with a unique numeric identifier automatically assigned when a row is added, has an EDLEVEL column that permits only the values C, H and N, and permits inserts only when a corresponding value for the employees department exists in the DEPARTMENT table. Which of the following CREATE statements will successfully create this table?（）

单项选择题 When defining a referential constraint between the parent table T2 and the dependent table T1, which of the following is true?（）

单项选择题 Given the following two tables: TAB1 C1 C2 A 11 B 12 C 13 TAB2 CX CY A 21 C 22 D 23 The following results are desired: C1 C2 CX CY A 11 A 21 C 13 C 22 -- --D 23 Which of the following queries will yield the desired results?（）