Question

I have a table named categories, which contains ID(long), Name(varchar(50)), parentID(long), and shownByDefault(boolean) columns.

This table contains 554 records. All the shownByDefaultValues are ‘false’.
When I execute ‘select id, name from categories’, pg returns me all the categories, orderer by its id.
Then I update some of the rows of the table(‘update categories set shownByDefault where parentId = 1’), update OK.
Then, when I try to execute the first query, which returns all the categories, they are returner with a very weird order.
I do not have problem to add ‘order by’, but since I am using JPA to get this values, anyone knows what the problem is or if there is a way to fix this?

Answer 1

That’s not a problem. The order of rows returned by a SQL SELECT is undefined unless it has an ORDER BY. The order you get them is usually influenced by the order they are stored in the table and/or the indices that are used by the statement.

So depending on that order without using ORDER BY is a very, very bad idea.

If you need them in some order, simply specify that.

It is important that a table is a set of rows and not a sequence of rows.