null mysql

I. Basic1.serialize: Serialize a class, just save the properties of the class, so you also need to deserialize the unserialize when the class is included.2. For converting an array to object, this conversion is called an orphan class because there

1. Connecting to the database server$./mysql-h Host_name-u User_name-p -H HOST_NAME (--host=host_name), the connected database hostname, can be omitted if it is on the local host. -U user_name (--user=user_name), database user name, on

For beginners of SQL, the concept of null values often creates confusion, and they often assume that null is the same thing as a MySQL empty string. This is not the case. For example, the following statement is completely different:mysql> INSERT

Add, modify, delete functions in the MySQL tutorial ALTER TABLE tabelname add new_field_id int (5) unsigned default 0 NOT NULL auto_increment, add primary key (NEW_FIELD_ID); Add a new column ALTER TABLE T2 add d timestamp;ALTER TABLE infos add

SQL alert adding, modifying, and deleting field syntax instancesThe syntax for ALTER TABLE is as follows: ALTER TABLE "TABLE_NAME"[Change Mode] The detailed wording of the [change mode] will vary according to the goal we want to achieve. In the

The simplest kind of joint query The code is as follows Copy Code SELECT * FROM table1 N, table2 i WHERE n.itemid = I.itemid Cases Promotion Site Table promotion_addr field: Name,id Telephone report

Basic usage The mysql stored procedure is gradually adding new functionality from the MySQL 5.0 start. Stored procedures are also more advantageous than disadvantages in practical applications. But the main thing is execution efficiency and SQL

One, union query usage The union query is simpler, as if the two tables were merged and the fields were combined If it is SELECT * FROM table1, table2 Words, two of the same fields will not be merged but Select A1 from table1 Union Select A1

Objective I believe we all know that implicit type conversions have the risk of being indexed, and that in the case of high concurrency and large amounts of data, the result of an index is very serious. Dragging the database down, and then crashing

In many cases, the database defaults are null, but the case is that the database values are empty rather than NULL when the program is processed. Note When a unique index is created, when the database will empty as multiple duplicate values, and the

Each line command ends with a semicolon (;) For MySQL, the first thing you have to keep in mind is that each line of its command is terminated with a semicolon (;), but when a row of MySQL is inserted into the PHP code, it is best to omit the

1, the method of declaring the primary key:You can add a primary key to a table when you create it, such as:CREATE TABLE tbl_name ([Field description omitted ...], PRIMARY KEY (index_col_name));You can also add a primary key to a table when you

A connection error occurred in MySQL: ERROR 1045 (28000): Access denied for user ---------------------------------------------------------------------------------- 1. Add User Shell>mysql Mysql>use MySQL Mysql>grant all privileges in *.* to '

Using indexes to improve query speed1. ForewordIn Web development, page templates, business logic (including caching, connection pooling) and database three parts, in which the database is responsible for executing SQL queries and returning query

set,enum data types are object of string type, where the set can contain up to 64 elements and can be arbitrarily taken to the elements in the collection. An enum is an element that can only be taken to a wood in a collection, containing up to 65,536

MySQL add field: ALTER TABLE ' User_movement_log ' add column Gatewayid int not null default 0 after ' RegionID ' (added after which field) To delete a field: ALTER TABLE ' user_movement_log ' drop column Gatewayid To

In addition to providing a servlet, Java EE provides a number of other features. Servlet developers may rarely use these features, reluctantly and without the time to replace their own simple servlet with a large Java server that exceeds the

Mysql MySQL Join Detailed Solution (C) by Dennis Dll 2004.1.29 Let's Create a table first. CREATE TABLE EMP ( ID int NOT NULL PRIMARY key, Name varchar (10) ); CREATE TABLE Emp_dept ( dept_id varchar (4) NOT NULL, emp_id int NOT NULL, Emp_name

Original: http://bbs.landingbj.com/t-0-243202-1.htmlBy default, MySQL sorts all group by col1, Col2, ...., and the method of querying is like specifying order by col1, col2, ... in a query.If you explicitly include an ORDER BY clause that contains

Mysql-day03One, MySQL storage engine1.1 Storage Engine Introduction: Is the MySQL database software comes with the function program,Each storage engine has different functions and data storage methodsThe storage engine handles the processor for the