A1:
| B and D. A is used in UPDATE operations. C is not a valid keyword. |
A2:
| A and D. A is valid. Wildcard characters are actually not required when you use LIKE; the search is effectively an equality test. B is invalid; NOT must precede LIKE. C is invalid; wildcards can be used with strings, not with numbers. D is valid; there is no limit to the number of wildcard characters that you can use in a search. |
A3:
| B. You use UPDATE when columns (as opposed to rows) are affected. A, DELETE, deletes entire rows. C, NULL, is not a statement; it represents no value and can be used with UPDATE to set a column to no value. |
A4:
| B. Primary keys may indeed be made up of more than one column. All the other statements are false. |