null mysql

First, Introduction Second, multi-table connection query Three, meet the conditions of connection query Four, sub-query First, IntroductionTopics in this section Multi-Table Connection query Compound conditional Join

An introductionConstraints are the same as the width of the data type, which are optional parametersRole: To ensure the integrity and consistency of dataMainly divided into:PRIMARY Key (PK) identifies the field as the primary key of the table and

Group replication is a new high-availability, high-expansion MySQL Cluster service.High consistency, based on the native replication and Paxos protocol group replication Technology, plug-in to provide consistent data security assurance;High fault

You can rename a column by using the change old_col_namecolumn_definition clause. When renaming, you need to give the old and new column names and columns the current type. For example, to change the name of an integer column from A to B, you need

First, the basic SELECT statement1. "*" NOTE: In the SELECT statement, use * To select all the columns, this is a habit should be resisted.While it saves time to enter column names, it also means more data is available than is really needed.

InstanceTry the following examples:[Email protected]# mysql-u root-p password;EnterPassword:*******Mysql> UseRunoob;DatabaseChangedmysql>CREATE TABLE Tcount_tbl- ( -Runoob_author varchar(40)Not NULL, -Runoob_count INT- );QueryOk, 0Rows

I encountered a problem when I was developing a project within the company:Select student_quality_id from student_quality where Mark_status=0 and batch_stauts in (2,3)The result encountered a student_quality_id that had been unable to find a

CREATE TABLE tab2 as (SELECT * from TAB1)The storage engine for this practice table also uses the server's default storage engine instead of the source table's storage engine, which copies the contents of the table together.CREATE talbe tab2

Source: http://www.cnblogs.com/zhuyp1015/p/3575823.html will use several tables mysql> DESC products;+------------+--------------+- -----+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |+------------+--------------+---

Usage of IS NULL statement in MySQL database Note that in MySQL, 0 or null means false and other values mean true. The default truth value of a Boolean operation is 1. The special handling of NULL is in the previous section, in order to determine

We have seen the SQL SELECT command using the WHERE clause to fetch data from the MySQL table. However, when we try to give the condition to compare the value of the field or column to NULL, it does not work correctly. To handle this situation,

1. Data preparationMysql> select * from student;+----+--------+----------+---------+-------------+| ID | name | Idcardno | Iscadre | Nickname |+----+--------+----------+---------+-------------+| 1 | Tom |       350020 | 1 | Big T || 2 | Jim |    3500

An introductionTopics in this sectionMulti-Table Connection queryCompound conditional Join QuerySub-queryPrepare tableCompany.employeeCompany.department#建表create Table Department (ID int,name varchar); CREATE TABLE employee (ID int primary KEY

MySQL field constraint Null,not null,default,auto_increment "comes from" no rules, inadequate surrounding area, everything is so. In MySQL, each field definition contains additional constraints or modifiers that can be used to increase the

MySQL floating-point and fixed-point types can be represented by the type name plus (m,d), m represents the total length of the value, D represents the length after the decimal point, and M and D are also known as precision and scale, such as float (

Multi-Table Query Multi-Table Connection query Compound conditional Join Query Sub-query First, prepare the table#建表create Table Department (ID int,name varchar (20) ; CREATE table employee (ID int primary KEY

Select *,if (sva=1, "male", "female") as Ssva from Taname where sva<> ""12.2. Control process functionsCase value when [compare-value] and then result [when [compare-value] then result ...] [ELSE result] END case [condition] then result [when

We already know that MySQL uses the SQL SELECT command and the WHERE clause to read data from a data table, but the command may not work correctly when the supplied query condition field is NULL.To handle this situation, MySQL provides three large

One: IntroductionTheme:Multi-Table Connection queryQualifying Connection QuerySub-queryPrepare table#Build TableCREATE TABLE Department (ID int,name varchar (20) ; CREATE table employee (ID int primary KEY auto_increment,name varchar (20), sex enum (

MySQL Master-slave replicationExperimental environmentMaster: 192.168.110.33From: 192.168.110.59Iptables and SELinux disabledMaster: Server-side1. Install and initialize# yum Install-y mysql-mysql-server#/etc/init.d/mysql start#