B+ tree stored procedures, triggers, substring and substr, and truncate and delete

One 、B+TREE Stored procedure
B+ A key design of tree , Let the size of a node of the tree be equal to the size of a block . Elements stored in nodes , Not an element , But one that can hold m An ordered array of elements .B+ Another design of the tree , Non leaf nodes only have index data and pointers to tree structures , Leaf nodes store specific data . In this way, non leaf nodes can store more index data , One 3~4 Layer of B+ Trees can index dozens T The data of the .B+ The tree also links the nodes of the same layer to form a two-way linked list , In this way, it has the ability of range query and flexible adjustment .B+ The data in each node in the tree is queried by the binary query algorithm .
Two 、 trigger stored procedure
A trigger is a database object related to table operations , When the trigger shows the specified event on the table , Call the object , That is, the operation event of the table triggers the trigger execution on the table .
stored procedure ： Execution efficiency and sql Code block encapsulation . Code block encapsulation means that we can organize multiple sql Put it together to carry out , Business logic can be encapsulated in stored procedures , This is not only conducive to maintenance , It's also efficient .
3、 ... and 、substring and substr The difference between
substring It's getting from start Bit start to end String between bits , and substr It's getting from start After bit start end Bit string ;（ Both methods involve start Bit string , The difference lies in subtring It doesn't contain end Bit string ,substr contain ）
Four 、truncate and dalete The difference between
1、truncate： Delete the contents of the table , Do not delete table structure , Release space
2、delete： Delete content , Do not delete table structure , But it doesn't release space