单项选择题 Which of the following can be used to ensure that once a row has been inserted in table TABLEX, the column MAINID in that row cannot be updated?（）

单项选择题 Given the following requirements:Create a table named TESTTAB, which has an identity column named ACTIVITYNO. Define the identity column to generate the values for the column by default. Start the values at 10 and increment by 10. Make the identity column unique. Which of the following CREATE statements will successfully create this table?（）

单项选择题 The following triggers were defined for table TAB1 in the order shown:CREATE TRIGGER trig_a AFTER UPDATE ON tab1 FOR EACH ROW UPDATE sale_tab SET sale_date = CURRENT DATE; CREATE TRIGGER trig_b AFTER UPDATE ON tab1 FOR EACH STATEMENT UPDATE invoice_tab SET invoice_date = CURRENT DATE; CREATE TRIGGER trig_c AFTER UPDATE ON tab1 FOR EACH ROW UPDATE shipping_tab SET ship_date = CURRENT DATE; CREATE TRIGGER trig_d AFTER UPDATE ON tab1 FOR EACH STATEMENT UPDATE billing_tab SETbilling_date = CURRENT DATE;If an event occurs that causes all of them to activate, which trigger will be activated first?（）