Relation R has schema:
CREATE TABLE R (
a INT PRIMARY KEY,
b INT DEFAULT 0,
c INT NOT NULL
);
R is currently empty. Develop a test that determines whether an insertion into R is currently legal. Then apply your test to determine which of the following INSERT statements is allowable.
a) INSERT INTO R(c) VALUES(0);
b) INSERT INTO R(a,b) VALUES(1,2);
c) INSERT INTO R(c,a,b) VALUES(3,4,5);
d) INSERT INTO R(b,c) VALUES(3,4);

Answers

Answer 1

Tthe following INSERT statements is allowable

b) INSERT INTO R(a,b) VALUES(1,2);c) INSERT INTO R(c,a,b) VALUES(3,4,5);

How to get the sentences

To determine whether an insertion into a table is legal, you need to ensure that:

The values provided satisfy the constraints defined in the schema (e.g., not null, default values, primary key uniqueness).

All columns that don't allow null values are included in the INSERT statement.

Given these rules, let's see which of the INSERT statements are allowable.

a) INSERT INTO R(c) VALUES(0);

This statement is NOT allowable. Column 'a' is a primary key and does not have a default value, so it must be included in every INSERT statement.

b) INSERT INTO R(a,b) VALUES(1,2);

This statement is allowable. Although column 'c' is not included, it's defined as NOT NULL, but it's okay here as column 'c' does have a default value (0), so this column will take the default value.

c) INSERT INTO R(c,a,b) VALUES(3,4,5);

This statement is allowable. All columns are included in the statement, and the values are acceptable according to the constraints defined in the schema.

d) INSERT INTO R(b,c) VALUES(3,4);

This statement is NOT allowable. Similar to the issue in statement a), column 'a' is a primary key, so it must be included in every INSERT statement.

In summary, the allowable statements are b) and c). Statements a) and d) are not allowable because they do not include a value for the primary key 'a'.

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