by index rowid

"by index rowid" is a clause used in SQLite queries to indicate that the result should be ordered by the index of the row IDs. This clause is typically used in conjunction with the "ORDER BY" clause and can be useful in optimizing queries that need to access rows in a specific order. However, it is important to note that not all tables in SQLite have an index on the row ID, so this clause may not always be applicable.

相关问题

table access by index rowid

"table access by index rowid" 是一种数据库查询的执行方式，它通过索引的行 ID（rowid）来访问表中的数据。

具体来说，这种查询方式首先需要根据查询条件使用索引查找到符合条件的行的 rowid，然后再使用这些 rowid 直接访问表中的数据，从而避免了全表扫描，提高了查询效率。

在 Oracle 数据库中，"table access by index rowid" 是一种常见的查询执行方式，但需要注意的是，如果表中的数据经常发生变化，rowid 可能会发生变化，从而导致查询结果错误。因此，在使用这种查询方式时，需要确保数据的稳定性。

Using index condition; Using where; Rowid-ordered scan

Using index condition, Using where, Rowid-ordered scan are terms related to performance analysis in database queries.

1. Using index condition: This term indicates that the query is using an index to filter the rows. It means that the query is able to utilize an index to efficiently retrieve only the necessary rows based on the specified conditions. This can improve the performance of the query by reducing the number of rows that need to be scanned.

2. Using where: This term indicates that the query is using a WHERE clause to filter the rows. It means that the query is applying additional conditions to further narrow down the result set. The WHERE clause is evaluated after the initial filtering using an index condition.

3. Rowid-ordered scan: This term indicates that the rows are being scanned in the order of their physical storage on disk. It means that the database is reading the rows in the order they are stored, which can be more efficient in certain cases.

Here is an example of a query and its performance analysis:

explain select * from employees where age > 30;

Explanation:
- Using index condition: The query is using an index on the "age" column to filter the rows where the age is greater than 30.
- Using where: The query is applying an additional condition using the WHERE clause.
- Rowid-ordered scan: The rows are being scanned in the order of their physical storage on disk.