Concatenated index from two columns === creating two indexes?

Question

PostgreSQL

Do I understand correctly that creating a Concatenated index from two columns

CREATE INDEX index_name
ON table_name (column1, column2);

Equally

CREATE INDEX index_name1
ON table_name (column1);

CREATE INDEX index_name2
ON table_name (column2);

Answer 1

In general, no. And in different DBMS differently. For example, in MySQL, an index (column1, column2) is also used to search only column1, but a separate index (column2) is required to search only column2.