null mysql

I have always been adhering to a point: through their hands real operation after the information is the most reliable, so in your reference to this small time please do not just "see", a simple look is not the truth drop ~ ~ ~ Motto: Paper on the

Null in the database means "no input data to (column) variables", that is, NULL in the database can distinguish between "no input data to (column) variables" and "Input data to (column) variables". And the input of the empty string, is here the

Generally, the entire string is used as the operation object, for example: search for a substring in a substring, obtain a substring, insert a substring at a certain position in the substring, and delete a substring. The required and sufficient

A string or string (string) is a finite sequence consisting of 0 or more characters. Generally recorded as s= ' a1a2 an ' (n>=0). It is the data type that represents text in the programming language. A string is usually used as an action object,

A string is usually used as an action object, such as finding a substring in a string, seeking a substring, inserting a substring at a point in a string, and deleting a substring. The necessary and sufficient condition for two strings to be equal is

For operations on string positions, the first position is marked as 1. ASCII (str) Returns the ASCII code value of the leftmost character of the string str. If Str is an empty string, returns 0. If STR is NULL, returns NULL. Mysql> Select ASCII (' 2

MySQL String Function EncyclopediaFor operations on string positions, the first position is marked as 1. ASCII (str) Returns the ASCII code value of the leftmost character of the string str. If Str is an empty string, returns 0. If STR is NULL,

One: Field modifier1:null and NOT NULL modifiersLet's take a look at this example.Mysql> CREATE TABLE worker (ID int not null,name varchar (8) Not null,pass varchar (a) not null);Mysql> INSERT into worker values (1, ' HA ', ' 123456 ');Mysql> INSERT

MYSQL getting started 6: MYSQL operator bitsCN.com MYSQL getting started 6: MYSQL operators Related links: MYSQL: Basic operations Http: // database/201212/173868 .html MYSQL 2: use regular expressions to search Http: // database/201212/173869

Copy others, just to keep learning Mysql's left, right, substr, instr truncate string, truncate floatMysql's left, right, substr, instr truncate string, truncate float //----------------------------------------------------------------- Select avg

//----------------------------------------------------------------- Select avg (stu_oder_percent) from tb_sch_collect Result: Avg (stu_oder_percent ): 60.60962 //----------------------------------------------------------------- Select left (avg (stu_

If the result length is greater than the server parameter max_allowed_packet, the string value function returns NULL. For operations on the string position, the first position is marked as 1. ASCII (str) returns the ASCII code value of the leftmost

Select *, if (SVA = 1, "male", "female") as ssva from tableame where id = 1Quote control flow Functions Case value when [compare-value] Then result [when [compare-value] Then result...] [else result] end case when [condition] Then result [when

MySQL field constraints: null, notnull, default, auto_increment bitsCN.com MySQL field constraints: null, not null, default, auto_increment In MySQL, each field definition contains additional constraints or modifiers, which can be used to add

Mysql intercepts one decimal point after bitsCN.com Copy others, just to keep learning Mysql's left, right, substr, instr truncate string, truncate floatMysql's left, right, substr, instr truncate string, truncate float //----------------------------

ASCII (STR)Returns the ASCII code value of the leftmost character of the string str. If Str is an empty string, returns 0. If STR is NULL, returns NULL. MySQL Tutorial > select ASCII (' 2 '); -> 50 Mysql> Select ASCII (2); -> 50 Mysql>

Mysql and other languages also have many operators, including arithmetic operators, comparison operators, logical operators, bitwise operators, etc. This article introduces the mysql operators, their priorities, and examples to coders, for more

MySQL management and optimization (3) operator arithmetic operators: Operators include +,-, *, % (mod function), and/(p function ). Comparison operator: Numbers are compared as floating-point numbers, and strings are compared in

This article describes how to understand and use the NULL value in MySQL, A friend may refer to the concept of NULL value as a common cause of confusion among SQL beginners. They often think that NULL is the same as an empty string. No! For example,

Difference between NULL and MySQL NULL strings bitsCN.com Difference between NULL and MySQL NULL strings We often see MySQL NULL strings and NULL values, but they are not a concept. The following describes the differences between NULL and MySQL