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Data manipulation language

1. MySQL's operator
   concept : Operators are symbols that tell MySQL to perform special arithmetic or logical operations.
   Arithmetic operators are used for various numerical operations
   + (addition),-(subtraction), * (multiplication), / (division), remainder (or modular operation, %)

select 1+2;加法
select 2-1;减法
select 2*3;乘法
select 5/3;除法
select 5 div 2;-- 做除法，结果为整数
select 5 % 2, mod(5,2);模运算

2. The
   concept of comparison operators : the result of a comparison operator is always 1 (true), 0 (false), or null.
   比较运算符可以用于比较数字和字符串
   

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Let me briefly introduce the usage of some simple operators
like operator, used to match strings. The syntax format is: expr like 匹配格式*If expr meets the matching conditions, the return value is 1 (true); otherwise, it returns 0 (false). If either expr or matching condition is null, the result is null.
The like operator can use the following two wildcards when matching:

• '%', matches any number of characters, even 0 characters.
• '_', only one character can be matched.
  The regexp operator is used to match strings. The syntax format is: expr regepxmatch conditions. If expr meets the matching condition, the return value is 1 (true); otherwise, it returns 0 (false). If either expr or matching condition is null, the result is null.
  The following wildcards are commonly used in regexp operators:
• '^', matches the string beginning with the character following the character.
• '$', matches the character string ending with the character after the character.
• '.', matches any single character.
• '[Put the character you want to match]', match any character in the square brackets.
• '*', matches 0 or more characters before it.

3. The
   concept of logical operators : In SQL, the results of the evaluation of all logical operators are true, false, or null.
   
4. Bit operation operator
   concept : The operands involved in the operation are operated on binary bits.
   
   After learning the operators in MySQL, let's take a look at the precedence of operators.
   
5. Escape characters in mysql
   
6. Insert data table

为表的所有字段插入数据，字段名列表默认是全部字段，也可以指定字段。

insert into 表名(字段名列表) values (值列表);

insert into 表名(字段名列表) values (值列表1),(值列表2),...,(值列表n);       同时插入多条记录。

7. Insert query results into the table

insert语句用来给数据表插入记录时，指定插入记录的列值。

insert into 表名1(字段名列表1) select(字段名列表2) from 表名2 where (条件表达式);

The table name 1 is the table to be inserted into the data, and the rest can be deduced by analogy.
statement: Field name list 1 and field name list 2 must have the same number of fields and the same data type; "conditional expression" specifies selectthe query conditions of the statement.

8. Modify table data

update 表名 set 字段名1=新值1, 字段名2=新值2,...,字段名n=新值n where (条件表达式);

note: Each "column-value" pair is separated by a comma, no comma is required after the last column

9. Delete table data

delete from 表名 where (要删除的某条数据);

Table name ¹
Field name list ²
(Value list 1), (Value list 2),..., (Value list n) ³

Data table query

• Select the specified field (column)

select 输出表达式;

• Define field alias

select 字段名 别名;
或者
select 字段名 as 别名; 

prompt: When you want to modify multiple field aliases, remember to separate them with commas.

• Replace data in query results

select 字段名1,字段名2,...,字段名n,
case 
     when 条件1 then 表达式1 
     when 条件2 then 表达式2
     ...
     else 表达式n
end
from 表名;

Today we will learn these first. Tomorrow we will write about MySQL and 常用函数hope that everyone will support it.

mysql injection common functions (on)

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1. The name of the data table where the record is inserted. ↩︎

2. Insert a list of field names in the record. ↩︎

3. Indicates to insert the value list of the field in n records. ↩︎