多项选择题
A.The tables being joined have NOT NULL columns.
B.The tables being joined have only matched data.
C.The columns being joined have NULL values.
D.The tables being joined have only unmatched data.
E.The tables being joined have both matched and unmatched data.
F.Only when the tables have a primary key-foreign key relationship.
单项选择题 You need to create a table named ORDERS that contains four columns: 1.an ORDER_ID column of number data type 2.a CUSTOMER_ID column of number data type 3.an ORDER_STATUS column that contains a character data type 4.a DATE_ORDERED column to contain the date the order was placed When a row is inserted into the table, if no value is provided for the status of the order, the value PENDING should be used instead. Which statement accomplishes this?（）
单项选择题 Examine the structure of the EMPLOYEES and NEW_EMPLOYEES tables: EMPLOYEES EMPLOYEE_ID NUMBER Primary Key FIRST_NAME VARCHAR2(25) LAST_NAME VARCHAR2(25) HIRE_DATE DATE NEW_EMPLOYEES EMPLOYEE_ID NUMBER Primary Key NAME VARCHAR2(60) Which DELETE statement is valid?（）
单项选择题 Which SQL statement returns a numeric value?（）