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Oracle has what table types, many novices are not very clear about this, in order to help you solve this problem, the following small series will explain in detail for everyone, there are people who need this can learn, I hope you can gain something.

More than 99% of Oracle tables are heap organized tables. When we execute create table by default, the default table type is heap table. For heaps. We can understand it as a simple storage space. We store data in piles, and his storage is disordered, like a pile of wood thrown into a pocket. So instead of asking us to get the data we want in the order it was stored, we read it in an unpredictable order. For example, when a heap table is scanned, oracle reads the data according to the order of hits, not according to the order of inserts and updates. The data will be read in a random manner, and the order of reading depends on other factors, such as parallelism, different optimizers, and so on.

Another type of table is called an indexed organization table (IOT); that is, a table stored in an index structure. The biggest difference between IOT and heap tables is that IOT data is stored and discharged in a gradual order. In contrast to heap tables, heap tables need to reserve enough space each time they are created to allow the table to create indexes, primary keys, and so on. However, IOT does not have this overhead of index primary key. For IOT, index is data, and data is index. However, we all know that indexes are complex data structures and have high maintenance costs, so the efficiency of heap organization tables will be relatively high. '

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