What is the core and most commonly used operation of the database?
If you want to know more about databases, you can click: SQL tutorial
The core and most commonly used operation of the database is addition, deletion, modification and query. Below we will introduce to you the specific operation syntax of adding, deleting and checking.
Database
Query database: show databases;
Create database: create database library name;
Delete database: drop database database name
Table
Create table: create table table name (field name data type [attribute] [index] 】)
View table structure: desc table name
View table: show tables
Insert data: insert into table name value()
View creation Table information: show create table table name
View the tables of the specified library: show tables where target library name
field
Add: alter table table name add field name data type [Attribute] [Index]
Insert a field after the specified position: alter table table name add field name data type [Attribute] [Index] after the specified field Name
Insert into the first position: alter table table name add field name data type [Attribute] [Index] first
Delete: alter table table name drop field name
Modification: alter table table name change old field new field data type [Attribute] [Index]
Conditional statement: > < >= <= != and or etc.
Data
Add: insert into table name value()
Delete: delete from table name (use with caution, delete the entire table data)
： machines U in Conditional statement
Operator query: select * from table name where id = 1 1
Select * from table name where id < 100
Logical query: select * from Table name where and condition
# SELECT * from table name where or condition
糊 query: Select * from table name when the name like 'value:%a% data) a% (find data starting with a) %a (find data ending with a)
Sorting and restricted query: select * from table name where order by column name desc Desc: indicates from Sort from big to small asc: Indicates sorting from small to large
select * form table name limit x,y (Column name) from table name
Count: Count the number of times data in a column or columns in the table is calculated
avg: Average value
Max: Maximum value
min: Minimum value
sum: The sum is generally used to calculate the price
Interval query: select * from table name where field between 0 and 10 Find data between 0 and 10
Group query: select displayed column from table name group by reference column
Select name,count(column) from table name group by name
select name,count( content) from table name group by name having count(content) > 5 Having is filtering on the basis of aggregation
Grouping queries are generally used together with aggregation queries
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