First, the concept of index
indexes in the database and directory similar books
- In a book, without having to read the entire book, you can use the directory to quickly find the information
- Contents of the book is a list of words, which shows the page number that contains each word of
database indexes - In the database, index the database program without having to scan the entire table, you can find the required data in which
- The index is a database table or a collection worth several columns, as well as physical identification logic pointer list of these pages worth of data
indexing advantages: You can quickly find the data
Disadvantages: take up hard disk resources
Second, the index role - After setting the appropriate index, fast database using a variety of positioning technology, can greatly accelerate the rate of inquiry
- Especially when large table or query involves multiple tables, queries can use the index to speed up to a thousand times
- IO read and write the database can reduce the cost, and the index can also reduce the cost of sorting the database
- The only guarantees data table data by creating a unique index
- You can speed up the connection between the table and the table
- When using grouping and sorting, grouping and sorting can greatly reduce the time
Third, the classification index
the ordinary index - This is the most basic index types, and it does not limit the uniqueness of such
unique index - This index and the previous "general index" is basically the same, but with one difference: all values of the indexed column can only occur once, that must be unique
- Unique index allowed to be null, but only once empty
primary key - Primary key is a unique index, but it must be designated as the "PRIMARY KEY"
full-text index - MySQL version 3.23.23 from the start to support full-text indexing and full-text search. In MySQL, the full-text index of the index type FULLTEXT, full-text index can be created on columns of type VARCHAR or TEXT
single index and multi-column index - Indexes can be created on a separate index, the index can be created in multiple columns on the
Fourth, create an index based on the principle of - Primary key, foreign key must have an index
- The amount of data of more than 300 rows of the table should be indexed
- TABLE often connected to the other tables in the connection field (foreign key) should be indexed
- Often appear in the Where clause field, especially in the field of large tables should be indexed
- Index should be built on a highly selective field
- Index should be built on a small field, even for large text fields long field, not to build index
- For large text fields and even long field full-text indexed, fulltext
- Uniqueness field is not too bad for indexing
- Too frequently updated fields unsuitable for creating an index
V. index creation method - According to business needs, after selecting a suitable index can be used to create an index CREATE INDEX
- CREATE INDEX plus the index keys can create various types of indexes
practical operation of the process
1. Create a plain index
Delete index
2. Create a unique index
to delete the index
"alter table" to create a unique index
Another way is when you create a table, on the definition of the index.
Create a table hobby
to hobby table to add data
to two tables associated with
this is a typical multi-table queries connected to
avoid redundant code may alias for the table
view Overview
is a virtual table, view data does not exist, just real table mapping data. Using screening conditions, grouping, sorting, and so produce a result set, stored in memory, and make persistent storage. (Only save maps)
view will take up less resources, equivalent to a soft connection, shortcuts
real data in the table changes, the view will change accordingly ensue.create view 视图名称 as 查询语句（select id，name，age） from 表名 where（条件） id=1 or id=5；The role of view: according to different users, create different views. Check under the authority of different views; enhance security; sql convenient operation.
Practical operation
to create a view
to see the view
stored procedure outlined
stored procedure: stored procedures used for software development direction
prevent code from being intercepted during network transmission, made security guarantees
original state: the code needs to be embedded sql statement: by connecting the drive (java is jdbc) ---- the sql statement as a parameter passed to the execution mysql database.
Stored procedures are written in the database, not the program.
Program by calling a stored procedure name to trigger operation (function similar to the shell), the
advantages: the amount of code optimization, reducing the amount of code,
transmission security, sql statement hidden
network optimization.