Database operations
Command line access to databases: mysql -u username -p password
Show Database: show databases
New Database: create database databaseName
Delete the database: drop databse databaseName
Select the database: use databaseName
View all data tables: show tables
View table structure: desc tablesName
Data Manipulation
增：insert into table (`field1`, `field2`...) values ('value1','value2'...)
删：delete from table where field1=value1
改：update tablename SET field1=value2 where field1=value1
check:
Query the user table all the data:
select * from user;
where conditions of inquiry:
select * from user where id = 1002
as query field Rename:
select name as 名字 from user where id = 1002
Sort by :
select * from user order by age, id asc
age and positive sequence id field arrangement (high priority field age)
select * from user order by id, age desc
age and arranged in order to id field (field id high priority)
Skip to limit the query data:
select * from user where id>0 limit n
Front of the display data of n
select * from user where id>0 limit m,n
Skip ahead and m show the next n data
Fuzzy query:
like +% is used (without%, 'like' equal to '=')
field contains the name 'ven'
select * from user where name LIKE "%ven%"
Lee name field begins with:
select * from user where name LIKE "Lee%"
the end of the name field Jun:
select * from user where name LIKE "%Jun"
Range query :
in the statement :( query data idzai () in)
select * from user where id in (1001,1002,1003)
between ... and statements: (a query id range 1001-1010 data)
select * from buser where id between 1001 and 1010
polymerization:
Statistical number of records: count (fidle)
select count(id) where id>1001
Summing a field: sum (fidle)
select sum(age) where id>1001
Field seeking average : avg (fidle)
select avg(age) where id>1001
Seeking a maximum value : max (fidle)
select max(age) where id>1001
Seeking the minimum value : min (fidle)
select min(age) where id>1001
UNION operator:
Results for SELECT statements are connected to two or more combinations of a set of results. More SELECT statements will delete duplicate data
select id,title from articles union select id, title from books order by id
Grouping query results: group by
On the name field grouping and statistics of the total number of fields of age
select name,count(age) from employee_tbl group by name
On the name field and a statistical average age grouping fields
select name,avg(age) from employee_tbl group by name
Statistics on the name field of the packet and the maximum age field
select name,max(age) from employee_tbl group by name
Statistics on the name field and a minimum age grouping fields
select name,min(age) from employee_tbl group by name
Field Grouping of name and age fields of statistics and
select name,sum(age) from employee_tbl group by name
having query
Field name and the field conditions and the statistical grouping of singin name <> 'Li'
select name,sum(singin) from employee_tbl group by name HAVING name <> '丽'
Note:
where 与 having：
where and having keywords used to set conditional expressions to filter query results, the difference is behind having polymerization can be followed
Function, and where not, are usually used in conjunction with having the keywords group by, the data represents packet filter
Connect using:
The connector (INNER JOIN): Get record matching the fields in the relationship between two tables
Left connecting (LEFT JOIN): Get the left table all records, even if no record corresponding to the right table matching.
Right connection (RIGHT JOIN): LEFT JOIN contrast with, for acquiring the right table all records, even if no record corresponding to the left table matching.
Data table is as follows:
The connecting use:
A query display table id, title and author and table id field b, a query for the table ID field = b table ID field
select a.id,a.title,a.author, b.id from books a inner join articles b on a.id = b.id
Left connect using:
Query left table ID field (Books) in id, title field and autho right table (Articles) content and the id field, the query condition is left = right table of the table ID field
select a.id,a.title,a.author, b.id,b.content from books a left join articles b on a.id = b.id
Note: the left connecting the left reads all the data of the data table, even if no corresponding data table on the right, as follows
The right connection to use:
Query left table ID field () in id, title fields, query left = right table of the table ID field
select a.id, a.content,b.id,b.title,b.author from articles a right join books b on a.id = b.id
Note: all data to the right of the right connection data table will be read, even if no data corresponding to the left side of the table; following
