null mysql

MySQL Index analysis and optimization solution 1. What is an index? Indexes are used to quickly search for records with specific values. All MySQL indexes are saved as B-trees. If no index exists, MySQL must scan all the records of the

I. Model IntroductionOne person corresponds to multiple addresses ).2. entity (the getter and setter methods are omitted)Public class person1ntab_sx {Private int personid;Private string name;Private int age;Private set addresses = new hashset

18.2.1 MySQL server has gone away errors related to Lost connection to server during query. The most common cause of the MySQL server has gone away error is that the server times out and closes the connection. By default, if nothing happens, the

Basic MySQL Data Table operation 3: A comprehensive example of basic mysql operations 1. Create a database mysql> create database company;mysql> use company; Ii. Create a table 1. Create an offices table mysql> create table offices -> ( ->

I. Basic select statements 1. Note for "*": In the SELECT statement, use * to select all columns, which should be resisted. Although saving the time for entering the column name, it also means that the data obtained is much more than the data

Reference: http://zxlm.cityk.cn/fh/viewthread.php? Tid = 1395 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

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

The following articles mainly introduce common MySQL commands and the collation of common MySQL commands. We all know that the proportion of commonly used MySQL commands in actual applications is relatively large, today, we will give you a detailed

Example of if in mysql statement bitsCN.com 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

Mysql character set setting has recently been working on a project related to mysql proxy, which involves parsing SQL statements. I didn't know much about mysql before. as the project progresses, I had to make up for it. Today, I suddenly saw

The following two functions can be used to concatenate the query result line fields of Mysql: 1concat function mysqlselectconcat (39; 139;, 39; 239;, 39; 339;) fromtest; + --------------------- + | concat (39; 139;, 39; 2 concatenate the query

This article mainly describes the example of using if in MySQL statements and the specific operation steps, this document demonstrates how to use the if statement in MySQL. The following describes the specific solution. I hope it will be helpful in

MySQL NULL value processing instance details, mysqlnull MySQL NULL value processing We already know that MySQL uses the SQL SELECT command and the WHERE clause to read data in the data table. However, when the provided query condition field is NULL,

MySQL uses if and mysqlif to determine 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

I. Basic SELECT statements1. Note for "*": in the SELECT statement, use * to SELECT all columns, which should be resisted.Although saving the time for entering the column name, it also means that the data obtained is much more than the data actually

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,

Introduced: 1. The database will only be connected if you perform select, UPDATE, delete, INSERT, etc. 2, the use of PDO pretreatment mode 3. Transaction processing 4, Error output The code is as follows Copy Code

MySQL tutorial is null usage 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 which animal is

1 Simple query is to display the contents of all the data rows in a data table; 2 Execute the FROM clause in the query to determine the data source (which is actually all rows and columns) to control the data columns to display 3 If there is

Must understand the SQL knowledge One, two table outer join query The existing two table A,b contents are as follows Mysql> select * from A; +------+------+ | ID | Col1 | +------+------+ | 1 | AA | | 2 | BB | | 3 | CC | +------+-