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Is primary key automatically indexed in postgresql?

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I created the table name as d with the identifier column as the primary key, and then simply inserted the records as shown in the output, but after extracting all the records, this output still shows the same as the order in which the records are inserted. but the conclusion, as we see now, is not in an ordered form.

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3 answers

PostgreSQL automatically creates an index for each unique constraint and primary key constraint to ensure uniqueness. Thus, there is no need to explicitly create an index for the primary key columns. (See CREATE INDEX for more information.)

Source: Docs

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but after retrieving all the records, this output is still displayed in the same way as the order in which the records are inserted

There is NO default sorting in order - even if the column has an index (which is really the case in Postgres: the primary key is supported by a unique index in the background)

Rows in a relational table are not sorted.

only (really: the only) way to get a specific order is to use ORDER BY

If you do not specify ORDER BY , the database can return rows in whatever order it wants - and this order can be changed at any time.

The order may vary for various reasons:

  • other sessions work with the same operator
  • updated table.
  • the execution plan is changing.
  • ...
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In addition to what others have said, Postgres does not have the concept of a "clustered index" like Microsoft SQL Server and other databases. You can cluster the index, but this is a one-time operation (until you call it again) and it will not support row clustering when editing, etc. See documents

. I came across the same thing as you, where I half expected the rows to be returned in the order of the primary key (although I did not insert them out of order, like you did, though). They returned after the initial insertion, but editing a post in Postgres seems to move the post to the end of the page, and the posts are out of order (I updated fields other than the primary key).

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Source: https://habr.com/ru/post/1265697/

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