Summary of SQL Statements

DML data manipulation language

• The select
  SELECT statement is used to select data from a table
  Syntax: SELECT column name FROM table name
          SELECT * FROM table name
  Asterisk (*) is a shortcut to select all columns
  
  Example: SELECT FristName,dress FROM transcript
  
  
• The select distinct
  keyword distinct is used to return only distinct values
  ​​Syntax: SELECT DISTINCT dress FROM transcript
  
  
• where
  conditionally selects data from a table
  Syntax: SELECT column name FROM table name WHERE column operator value
  Example: SELECT score FROM transcript WHERE score=78
          SELECT * FORM transcript WHERE dress='shanghai'
  
  
• and and or
  combine two or more conditions in the where clause. If
  A and B are established, the and operator displays a record;
  as long as one of A and B is established, the or operator displays a record;
  AND operator Example:
  SELECT * FORM transcript WHERE FirstName='yang' AND LastName='ming'
  OR Operator Example:
  SELECT * FORM transcript WHERE FirstName='yang' OR LastName='ming'
  
  
• ORDER BY is used to sort the result set; the
  default is to sort in ascending order, if you want to sort in descending order, use the DESC keyword;
  example: SELECT FirstName,score FORM transcript ORDER BY FirstName
           SELECT FirstName,score FORM transcript ORDER BY FirstName,score
          SELECT FirstName ,score FORM transcript ORDER BY FirstName DESC,score ASC
  
  
• The INSERT INTO statement is used to insert a new row into a table
  Syntax: INSERT INTO tablename VALUES (value1, value2........)
  Specify the columns into which data is to be inserted:
  INSERT INTO table_name (column1,column2 ......) VALUES (value 1, value 2.......)
  Example:
  INSERT INTO transcript VALUES (8,xin,yu,95)
  insert into transcript (ID_t,LastName,FirstName,score) values (9,yan,zhu,88)
  
  
• The UPDATE statement is used to modify data in a table
  Syntax: UPDATE table name SET column name = new value WHERE column name = some value
  Example: UPDATE transcript SET score = 87 WHERE ID_t = 8
  Several columns in a row:
  UPDATE transcript SET score = 89 ,LastName = 'jia',FirstName = 'wang' WHERE ID_t = 8
  
  
• delete语句用于删除表中的行;
  语法:DELETE FORM 表名称 WHERE 列名称 = 值
  实例:DELETE FORM transcript WHERE LastName = 'jia'
  删除所有的行
  delete form table_name
  delete * form table_name
  
  
  
  

1. create DB  创建数据库
   语法:CREATE DATABASE database_name
   实际:创建一个名为my_db的数据库
   CREATE DATABASE my_db
2. create table 创建数据库中表
   
   创建新表
   语法:CREATE TABLE 表名称
   (
   列名称1 数据类型,
   列名称2 数据类型,
   列名称3 数据类型,
   ......
   )
   
   实例:创建名为transcript的表
   CREATE TABLE transcript
   (
   ID_t int,
   LastName varchar(255),
   FirstName varchar(255),
   dress varchar(255),
   score varchar(255)
   )
   
   NOT NULL 约束
   强制列或者字段不接受空值
   例如:
   CREATE TABLE transcript
   (
   ID_t int NOT NULL,
   LastName varchar(255) NOT NULL,
   FirstName varchar(255),
   dress varchar(255),
   score varchar(255) NOT NULL
   )
   
   使用旧表创建新表
   create table new_tab like old_tab
   
   PRIMARY KEY 主键必须包含唯一的值;
   每个表都应该且只能有一个主键;
   create table student
   (
   sid int not null,
   sname varchar(255)
   ...
   primary key(sid)
   )
   
   添加主键:
   alter table table_name add primary key(...)
   删除主键:
   alter table table_name drop primary key(...)
   
   create index 在表中创建索引
   CREATE INDEX index_name ON table_name(column_name)
   在表示创建一个唯一的索引
   CREATE UNIQUE INDEX index_name ON table_name(column_name)
   
   实例:CREATE INDEX student_index ON student(Sname)
   
   drop index 删除索引
   DROP INDEX index_name 
   实例:
   DROP INDEX student_index 
   
   
   
   
   
   
3. drop 删除数据库
   DROP DATABASE database_name
   实例:DROP DATABASE my_db
   
   DROP table 删除表
   DROP TABLE table_name
   实例:drop table transcript
   
   truncate table 只删除表内数据,不删除表本身
   TRUNCATE TABLE transcript
   
   
4. Alter
   ALTER TABLE 在已有的表中添加,修改或者删除列
   添加:
   ALTER TABLE table_name
   ADD column_name datatype
   删除:
   ALTER TABLE table_name
   DROP COLUMN column_name (某些数据库不允许此种删除方式)
   修改:
   ALTER TABLE table_name
   ALTER COLUMN column_name datatype
   
   实例:
   在已知的表中添加Brithday列
   ALTER TABLE transcript
   ADD Brithday date
   
   
5. TOP 用于规定要返回的记录的数目;
   
   
6. like  WHERE子句中搜索列中的指定模式
   语法:SELECT column_name FROM table_name WHERE column_name LIKE  pattern
   
   SELECT * FROM Persons
   WHERE City LIKE 'N%'
   
   
   
7. IN  IN 操作符允许我们在 WHERE 子句中规定多个值
   SELECT column_name FROM table_name WHERE column_name IN (value1,value2...)
   
   SELECT * FROM Persons WHERE LastName IN ('Adams','Carter')
   
   
   
8.  BETWEEN ... AND
   操作符 BETWEEN ... AND 会选取介于两个值之间的数据范围。这些值可以是数值、文本或者日期
   SELECT column_name(s)
   FROM table_name
   WHERE column_name
   BETWEEN value1 AND value2
   
   
9. AS
   表的 SQL Alias 语法
   SELECT column_name(s)
   FROM table_name
   AS alias_name
   
   列的As语法
   SELECT column_name AS as_name FROM table_name
   
   SELECT po.OrderID, p.LastName, p.FirstName
   FROM Persons AS p, Product_Orders AS po
   WHERE p.LastName='Adams' AND p.FirstName='John'
   
   
   
10. SQL join 用于根据两个或多个表中的列之间的关系，从这些表中查询数据
    
    JOIN: 如果表中有至少一个匹配，则返回行
    LEFT JOIN: 即使右表中没有匹配，也从左表返回所有的行
    RIGHT JOIN: 即使左表中没有匹配，也从右表返回所有的行
    FULL JOIN: 只要其中一个表中存在匹配，就返回行