null mysql

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MySQL common functions _ MySQL

MySQL common function bitsCN.com string function CONCAT (str1, str2,...) returns the string generated by the connection parameter. If any parameter is NULL, the return value is NULL. [SQL]View plaincopy Mysql> % 20 SELECT % 20 CONCAT ('My, %

MySQL functions and usage examples _ MySQL

MySQL functions and Usage examples String functions ASCII (str)Returns the ASCII value of the first character of the string 'str' (0 is returned when 'str' is an empty string)Mysql> select ASCII ('2 ');-> 50Mysql> select ASCII (2 );-> 50Mysql>

Practical application of MySQL conditional select case

The following articles mainly describe the practical application of MySQL conditional select case. This article does not closely introduce the actual application code example, it also lists the items worth your attention in the actual operation of

MySQL floating point representation

MySQL floating point representation MySQL floating-point and fixed-point types can be expressed by the type name plus (M, D). M indicates the total length of the value, and D indicates the length after the decimal point, M and D are also called

Mysql is null usage

Mysql tutorial is null usage Note that in mysql, 0 or null means false while other values mean true. The default true value of Boolean operations is 1. The special processing of null is in the previous chapter. To determine which animal is no longer

Hive metadata Parsing

Hive metadata parsing this article is a Hive metadata table prepared by the author. If there is any inaccuracy, please pat it. I will add it later. 1. hive0.11 meta data Table Summary online Hive0.11metastore includes the following 39 tables, mainly

MySQL floating point type, mysql floating point type

MySQL floating point type, mysql floating point type MySQL floating-point and fixed-point types can be expressed by the type name plus (M, D). M indicates the total length of the value, and D indicates the length after the decimal point, M and D are

MySQL learning notes-data definition table constraints, paging method summary, mysql learning notes

MySQL learning notes-data definition table constraints, paging method summary, mysql learning notes This article describes the data definition table constraints and paging methods of MySQL learning notes. We will share this with you for your

and Yan 18 study php-27th Day-about the difference between the inner connection

With Yan 18 study php-27th Day-the difference between the right and left inner joins /** Yan 18 public benefit PHP Training Classroom Address: YY Channel 88354001 Learning Community: www.zixue.it **/ Mysql> CREATE TABLE Boy ( Bname varchar (20),

MSYQL case when THEN control process function Tutorial

Case value when [compare-value] THEN result [when [compare-value] THEN result ...] [ELSE result] When [condition] THEN result [when [condition] THEN result ...] [ELSE result] EndIn the return result of the first scenario, Value=compare-value. The

MySQL GROUP by function tutorial

GROUP by (aggregate) functionsThis chapter discusses group (set) functions for a set of numeric operations. Unless otherwise stated, the group function ignores NULL values. If you use a group function in a statement that does not contain a roup by

MySQL database from delete library to run MySQL multi-table query

An introductionTopics in this sectionMulti-Table Connection queryCompound conditional Join QuerySub-queryPrepare tableCompany.employeeCompany.department#Build TableCREATE TABLE Department (ID int,name varchar (20) ; CREATE table employee (ID int

MySQL Master-slave replication

################## # # MySQL master copy # # ##################1, MySQL master-slave copy basic working principle:The master server changes the record to her binary log, copies the binary log of the primary server from the server to its intermediate

MySQL in contact, Group_concat, CONCAT_WS, repeat

Yi, CONCAT (str1,str2,...)Returns the string that results from the connection parameter. If any one of the arguments is NULL, the return value is null.Mysql> Select Concat (' One ', ' one ', ' $ '); +------------------------+| Concat (' One ', ' a ',

MySQL database permissions, index basic operations

How to close the database:1. Graceful way to close the database:mysqladmin-uroot-p123456 shutdown2. Script Close:/etc/init.d/mysqld stop3. Method of using kill signal (preferably not used)KILL-USR2 ' Cat path/pid 'History does not record historical

Usage of the is null statement in mysql

Usage of the is null statement in the mysql database Note that in mysql, 0 or null means false while other values mean true. The default true value of Boolean operations is 1. The special processing of null is in the previous chapter. To determine

Mysql string connection Function

1. CONCAT (str1, str2 ,...) Returns the string generated by the connection parameter. If any parameter is NULL, the return value is NULL. Mysqlselectconcat (112233, 33); ------------------------ | concat (, 33) | -------------------------- | --------

Example of using if in mysql statements

Select *, if (sva = 1, "male", "female") as ssva from taname where sva <> "" 12.2. Control Flow FunctionsCASE value WHEN [compare-value] THEN result [WHEN [compare-value] THEN result...] [ELSE result] end case when [condition] THEN result [WHEN

Basic MySQL Data Table operation 3: comprehensive example

Basic MySQL Data Table operation 3: comprehensive example 1. Create a database mysql> create database company;mysql> use company;  Ii. Create a table 1. Create an offices table mysql> create table offices -> ( -> officeCode int(10) NOT NULL

Practical application of MySQL condition selectcase

The following articles mainly describe the practical application of MySQL conditional selectcase. This article does not closely introduce the actual application code example, it also lists the items worth your attention in the actual operation of

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