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Tip 1: PRIMARY KEY(x, id), INDEX(id) -- where `id` is `AUTO_INCREMENT` is perfectly valid. It has the performance advantage of being more efficient when many queries need to find multiple rows WHERE x = 123. That is, it is slightly more efficient than the 'obvious' PRIMARY KEY(id), INDEX(x, id) The only rule about AUTO_INCREMENT (for InnoDB) is that ...


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some say, cluster index stores the whole records in deepest leaf of index. Yes this is correct. The leaf pages of the clustered index contain the actual table rows. This is the actual data. There is no other primary copy of it held elsewhere. The leaf pages also allocate a few bytes to hold the address (file and page) of the next and previous pages in ...


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This can get confusing for people to wrap their heads around. Let's get a couple of points clear in MS SQL Server. MS SQL Server has 2 types of tables: Heaps and Clustered Indexes. A heap has no order what so ever to it. Imagine taking a thousand names and throwing them in the air, then scrambling them around. That's essentially a heap. A heap uses RID ...


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No. If your table has the InnoDB engine and the PRIMARY KEY is (pet_id), then defining a secondary index as (person_id) or (person_id, pet_id) makes no difference. The index includes the pet_id column as well so values are sorted as (person_id, pet_id) in both cases. A query like the one you have: SELECT pet_id FROM yourtable WHERE person_id = 127 ORDER ...


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According to the MySQL Documentation on the Clustered and Secondary Indexes How Secondary Indexes Relate to the Clustered Index All indexes other than the clustered index are known as secondary indexes. In InnoDB, each record in a secondary index contains the primary key columns for the row, as well as the columns specified for the secondary index. ...



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