Oracle, SQL Foundation

Because use Oracle Will use SQL Statement all first look SQL sentence

1. basic SQL sentence

1. Inquire about

• select * from+ Table name （ Query the data of all columns in the table ）
  demonstration ：Select * from tb_stu
• select Name , Name from + Table name （ Query the contents of a column , Be careful ： Query multiple columns , Column names are separated by commas ）
  demonstration ：select sno,sname from tb_stu
• Select * from Table name where Name + Operator / Logical expression + value （ Query... According to the conditions ）
  demonstration ：Select * from tb_stu where age>20
  demonstration ：Select * from tb_stu where age=20
  demonstration ：Select * from tb_stu where age>20 and age<30
  demonstration ：Select * from tb_stu where between 20 and 30 and sex=‘ male ’

2. Fuzzy query

• select * from Table name where Query criteria
  demonstration ：select * from tb_stu where name like ‘% silly %’

3. increase

• Insert multiple data at a time ：
  insert into Table name （ Name 1, Name 2, Name 3……）
  values （ value 1, value 2, value 3.….）,
  （ value 1, value 2, value 3.….）,
  （ value 1, value 2, value 3.….）
  demonstration ：insert into Students (tid,name,sex,age)
  values(1,‘ Mei Chaofeng ’,‘ Woman ’,22)
• select( value 1, value 2, value 3) union,
• select( value 1, value 2, value 3),

4. Delete

• delete from Table name （ Delete all data in the table ）

• delete from Table name Where Delete the condition （ Delete data according to conditions ）

• demonstration :delete from tb_stu where name=‘ Zhang San ’

5. modify
   update Table name set Field 1= value 1, Field 2= value 2 where sid=1;

6. Create table ：
   create table Table name ( Field 1 data type , Field 2 data type );

7. Delete table
   drop table Table name ;

2.SQL Language introduction

2.1 SQL Language

sql(Structured Query Language) ： Structured query language . It's a special programming language , Is a database query and programming language , For data access and query 、 Update and manage relational databases .

2.2 SQL The composition of language

1. Structured query language includes the following 6 Parts of ：

• Data query language (DQL)： Also known as " Data element checking statement ". Common keywords ： select, where,order by, group by #I having,
• Data operation language (DML)： This statement includes verbs iinsert、update and delete. They are used to add 、 Modification and deletion .
• Transaction control language (TCL)： This statement ensures that DML All rows of the table affected by the statement are updated in time . Include commit Submit ） command 、save point( Save it ） command 、rollback（ Roll back ） command
• Data control language (DCL)： Its sentences are passed through grant or revoke Realize the authority control , Determine the access of individual users and user groups to database objects .
• Data definition language (DDL)： Its sentences include verbs cteate alert and drop. Create a new table or modify it in the database 、 Delete table (create table or droptable)
• Pointer control language (CCL)： Its statement , image declare cursor, fetch into #I update where For actions that are unique to one or more forms .

3.Oracle data type

Create table time , You must specify a data type for each column

3.1 Character data type ：

• char: Solid transformation , Length range ：1-2000 byte ; When a fixed length string is required , all char data type ,char The alphanumeric data type stores alphanumeric values
• varchar2: variable , Length range ：1-4000 byte ;VARCHAR2 The alphanumeric data type stores alphanumeric values
• long: variable ： Length range ：2GB;LONG Data types store variable length character data ,LONG Data types can store up to 2GB

3.2 Numerical data type .

number： Integer and non integer are number, Use number You can specify number The accuracy of , The highest accuracy is 38 position .

• Integer representation ：sid number(5)/ digit
• Non integer representation ：sid number(5,3);5 For integers
  The total length of bits and decimal places is 5,3 Representing decimal places
  The maximum length is 3, The maximum length of integer bits is ：5-
  3=2.
  99.999

3.3 Date data type .

• date： It can be accurate to seconds , such as ：1 Hours 1 branch 1 second .
• timestamp： The second value can be accurate to the decimal point 6 position , such as ：1 Hours 1 branch 1.111111 second

4.Oracle Supported by SQL The operator

4.1 arithmetic operator

• Arithmetic operators are used to perform numerical calculations
• Can be in SQL Use arithmetic expressions in statements , Arithmetic expressions consist of column names of numeric data types 、 Numeric constants and arithmetic operators that connect them
• Arithmetic operators include addition (+)、 reduce (-)、 ride (*)、 except (/)
  Case study

SQL> SELECT itemdesc, max_level - qty_hand avble_limit 
     FROM itemfile WHERE p_category='spares';

SQL > SELECT itemdesc, itemrate*(max_level - qty_hand)
      FROM itemfile 
      WHERE p_category='spares';

4.2 Comparison operator

• The comparison operator is used to compare the values of two expressions
• The comparison operators include =、!=、<、>、<=、>=、BETWEEN…AND、IN、LIKE and IS NULL etc.
  is null The role of ：
• effect ：is null Use to determine whether a column is empty

Case study

SQL> SELECT itemdesc, re_level
     FROM  itemfile
     WHERE qty_hand < max_level/2;

SQL> SELECT orderno FROM order_master 
     WHERE del_date IN (‘06-1 month -05’,‘05-2 month -05');

4.3 Logical operators

• Logical operators are used to combine the results of multiple calculation operations to generate one true or false result .
• Logical operators include and (AND)、 or (OR) He Fei (NOT).

Case study

SQL> SELECT * FROM order_master 
     WHERE odate > ‘10-5 month -05' 
     AND del_date < ‘26-5 month -05’;

-- Show  2005-5 month -10  to  2005-5 month -26 Order information for 

4.4 Set operators

• The set operator combines the results of two queries into one result .
• Set operators have ：union、union all;
• union： If the query results to be combined are the same , Only -
  One ;
• union all： Display all the query results to be composed .

--union
select 'a' from dual
union
select 'b' from dual;
--union all
select 'a' from dual
union all
select 'b' from dual;

4.5 Join operators

• Join operators are used to combine multiple strings or data values into one string
  Case study

-- And merge the employee number and name into the same column , Work and salary are merged into the same column 
select empno || ename  Number and name ,job ||sal from emp;

5. Pseudo column

5.1 Pseudo column overview

• Pseudo column ： seeing the name of a thing one thinks of its function , Disguised column , Hidden columns . Implicit existence , Can be explicitly called .
• oracle Pseudo columns in are like columns in a table , But it didn't
  There are stored in the table ;
• Pseudo columns can be queried from the table , But you can't insert 、 Update and delete
  Divide by their values .
• Common pseudo columns are rowid and rowunm.

5.2 Pseudo column -rowid.

oracle Every row of data in the database table has a unique -
Identifier , Otherwise known as rowid, stay oracle Inside usually
It is used to access data .
rowid need 10 Bytes of storage space , And use 18 Characters
To display . This value indicates that the data in this row is oracle In the database
Specific physical location of .
Show pseudo columns rowid:rowid

-- Pseudo column rowid
select a.rowid,a.* from emp a;

5.3 Pseudo column -rownum.

• stay Oracle It's executed inside insert During operation ,oracle According to insert The order of priority , take rownum Assign to each row of data , And it is fixed .
• oracle The pseudo column inside rownum and sqlserver The identification column inside is a little similar .
• Pseudo column rownum It can only act on less than and equal signs and less than and equal signs , Cannot act on the greater than sign .
• Show pseudo columns rownum、rownum

-- Pseudo column rownum
select b.*,rownum from(
       select a.*,rownum from emp a
) b order by empno desc;

6. Pagination *

stay Oracle It uses pseudo columns rownum Achieve the effect of paging

--（ The first page is displayed by default , Number of pieces 5）
select b.* from (
       select a.*,rownum as rid from emp a 
)b where b.rid between 6 and 10;

7. False watch .

• False watch ： seeing the name of a thing one thinks of its function . Camouflaged watch . Implicit existence , Sure
  Explicit call .
• Oracle The pseudo table in is ：dual;
• Because in Oracle Inside select It must be followed by from keyword , When select and from Syntax errors will be reported when it exists alone , Pseudo table can solve this problem .

-- seek 1+1 And .
select 1+1 from dual;
select 'a'

--dual  False watch 
select 'abc' from dual

8. constraint .
- constraint ： Primary key 、 Check 、 only 、 Non empty 、 The default value is 、 Outside
key .

create table tb_01(
	sid number primary key,-- Primary key constraint 
	sname varchar2(10) unique,-- Unique constraint 
	sex varchar2(10) check(sex=' male ’ or sex=' Woman "),-- Check constraint 
	age number(2) check(age>=18 and age<=100) not null,-- Non empty constraint 
	address varchar2(10) default ' Changsha '-- Default constraint 
)