'and this constraint create a unique index for accessing the table faster. ' meaning pls?

Question

In the explanation for Primary Key, what does the last line mean - 'and this constraint create a unique index for accessing the table faster.
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Thanks in advance.

Answer 1

indexing a column in SQL is like the index at the back of a book, instead of searching the book for a word, you check the index and it gives you the page number.

if you search a non indexed column it's like searching through the book and it takes longer.