Select two transaction isolation levels supported in PostgreSQL.

A. DIRTY READ

B. READ COMMITTED

C. REPEATABLE READ

D. PHANTOM READ

E. SERIALIZABLE

PostgreSQL can use an index to access a table. Select two incorrect statements about indexes.

A. An index is created by 'CREATE INDEX', and deleted by 'DROP INDEX'.

B. By using an index effectively, searching and sorting performs faster.

C. There are B-tree, Hash, R-tree and GiST index types.

D. By creating an index, performance always improves.

E. Creating an unused index does not affect the performance of a database at all.

The table "tbl" is defined below such that it could only store non-negative integers in the column "nn". Select the keyword that is applicable for the underlined blank. CREATE natural_number AS DECIMAL CHECK (VALUE >= 0); CREATE TABLE tbl(nn natural_number);

A. VIEW

B. SCHEMA

C. RULE

D. TYPE

E. DOMAIN

Select the most suitable statement about PostgreSQL from below.

A. There are PostgreSQL GPL license versions and commercial license versions.

B. You need to be pre-registered to use PostgreSQL.

C. PostgreSQL can be used by everyone free of charge for any purpose, be it private, commercial, or academic.

D. You can use PostgreSQL for free; however, the source code is not open to the public.

E. PostgreSQL is shareware.

Select two suitable statements about postgresql.conf configuration.

A. A line that starts with ! (exclamation mark) is interpreted as a comment.

B. You can have different parameters for the same option to configure each database differently.

C. The timing of when a change in any value is reflected is different depending on the configuration parameter.

D. All options have no default values. Therefore, all of them must be set specifically and thoroughly.

E. As a boolean value, any of the following can be used: TRUE, FALSE, ON, OFF, YES, NO, 0.1