Study notes 22/1/17

Learning notes

One 、 Program code block

1. Grammatical structure

-- Grammatical structure 
DECLARE
  -- Place of declaration （ Declare variables 、 Constant 、 Cursors, etc ）, This one can be omitted 
BEGIN
	--  Logical block of code execution 
  EXCEPTION
		-- Logic for handling exceptions 
END;
  -- Program end statement 
	
BEGIN
  DBMS_OUTPUT.put_line('HELLO WORLD');
END;	

All languages are from hello world Start ;

notes ：1. Remember to add a semicolon after each line of code ;
2.end Finally, be sure to add a semicolon as the end .

2. Variable

（1） Query through a given variable

DECLARE
        V_EMPNO NUMBER;
				V_ENAME VARCHAR2(30);
				V_SAL NUMBER;
BEGIN
        V_EMPNO :=7369;     -- Note the assignment syntax 
				
				SELECT T.ENAME,T.SAL          
				INTO V_ENAME,V_SAL
				
		/* SELECT T.ENAME  The inserted data of variables should correspond to  INTO V_ENAME */
				FROM EMP T
				WHERE T.EMPNO = V_EMPNO;	
				
				DBMS_OUTPUT.put_line(V_EMPNO||' '||V_ENAME||' '||V_SAL);	
END;

What you need to pay attention to when defining variables ：

     Variable naming rule , It's usually  V_  start 

1. Statement / When defining variables , If the definition is varchar Type of , That must be given length ,
If number Data of type , You can give it or not ,
If it is date Data of type , You don't have to give the length ;
2、 After defining the length of the variable , This variable cannot be assigned more than this length ;
3、 What types of variables are defined , What type of value should be assigned when assigning values ;
4、 Defines a variable , A semicolon is required at the end to indicate the end .

SELECT … INTO … Something to watch out for ：

1、 The result of our query Must be a row of data , It can't be 0 One or more lines ;
2、INTO This is followed by variables , The use is to SELECT The fields found after the query / The columns are put into variables in turn ;
3、INTO The order and number of the following variables must be the same as SELECT The order and number of fields in the subsequent query are consistent .

eg： Receive an employee's number （7788）, Name of the employee ,
Position , The entry date is printed （DBMS_OUTPUT.put_line）

DECLARE 
          V_EMPNO NUMBER;
					V_ENAME VARCHAR2(10);
					V_JOB VARCHAR2(9);
					V_HIREDATE DATE;
BEGIN 
	V_EMPNO := 7788;
	
	SELECT E.ENAME
	       ,E.JOB
				 ,E.HIREDATE
	INTO V_ENAME
	     ,V_JOB
			 ,V_HIREDATE
	FROM EMP E  
	WHERE V_EMPNO = E.EMPNO;
	
	DBMS_OUTPUT.put_line(V_ENAME);
	DBMS_OUTPUT.put_line(V_JOB);
	DBMS_OUTPUT.put_line(V_HIREDATE);   -- American date , The year of the sun and the moon 
	DBMS_OUTPUT.put_line(TO_CHAR(V_HIREDATE,'YYYY-MM-DD DAY'));
	-- Limited format output , Add the day of the week 
END;

（2） Query through input variables （ Use & Symbol ）

DECLARE 
          V_EMPNO NUMBER;
          V_ENAME VARCHAR2(10);
          V_JOB VARCHAR2(9);
          V_HIREDATE DATE;
BEGIN 
	--&  The function of this symbol is to pop up a data transfer window ,
	-- Text message followed “input_empno” As a reminder 
  V_EMPNO := &input_empno;
  
  SELECT E.ENAME
         ,E.JOB
         ,E.HIREDATE
  INTO V_ENAME
       ,V_JOB
       ,V_HIREDATE
  FROM EMP E  
  WHERE V_EMPNO = E.EMPNO;
  
  DBMS_OUTPUT.put_line(V_ENAME);
  DBMS_OUTPUT.put_line(V_JOB);
  DBMS_OUTPUT.put_line(V_HIREDATE);   -- American date , The year of the sun and the moon 
  DBMS_OUTPUT.put_line(TO_CHAR(V_HIREDATE,'YYYY-MM-DD DAY'));
  -- Limited format output , Add the day of the week 
END;

SELECT * FROM EMP;

Be careful ：

• When inputting data manually, you should pay attention to the input type
• Such as the input VARCHAR2 Type should be enclosed in single quotation marks ,
• Input date Type should be used to_date function , You can't type in number Data of type

eg：

DECLARE
 V_STR VARCHAR2(30);
 V_DATE DATE;
 V_NUM  NUMBER;
BEGIN
	V_STR := &INPUT_STR;   -- Input with single quotation marks 
	V_DATE := &INPUT_DATE;  -- The date type should be converted when entering 
	--to_date（） function 
	V_NUM := &INPUT_NUM;
	
	DBMS_OUTPUT.put_line(V_STR);
	DBMS_OUTPUT.put_line(V_DATE);
	DBMS_OUTPUT.put_line(V_NUM);
END; 

eg： According to the entered employee number , Output employee's bonus , If blank, output 0;

DECLARE
 V_EMPNO VARCHAR2(4);
 V_COMM NUMBER;
BEGIN
	V_EMPNO := &input_empno;   
	
	SELECT E.COMM
	INTO V_COMM
	FROM EMP E
	WHERE E.EMPNO = V_EMPNO;
	
	DBMS_OUTPUT.put_line(NVL(V_COMM,0));
END;  

（3） Variable declaration type

• %type
• %rowtype
• Constant constant

a.%type

• %type ： Can be used to determine the data type
  eg： According to the entered employee number , Output employee's bonus , If blank, output 0;

DECLARE
 V_EMPNO EMP.EMPNO%TYPE;
 V_COMM EMP.COMM%TYPE;
BEGIN
	V_EMPNO := &input_empno;   
	
	SELECT E.COMM
	INTO V_COMM
	FROM EMP E
	WHERE E.EMPNO = V_EMPNO;
	
	DBMS_OUTPUT.put_line(NVL(V_COMM,0));
END;  

b.%rowtype

• %rowtype： Refer to the data type and length of all fields in a table in the database ;

eg： According to the entered employee number , Output employee's bonus , If blank, output 0;

DECLARE
 V_EMP EMP%ROWTYPE;
BEGIN
	V_EMP.EMPNO := &input_empno;   
	
	SELECT E.COMM
	INTO V_EMP.COMM
	FROM EMP E
	WHERE E.EMPNO = V_EMP.EMPNO;
	
	DBMS_OUTPUT.put_line(NVL(V_EMP.COMM,0));
END; 

Be careful ：

• When using %rowtype when , It is equivalent to using the field name of an entire table as a variable to declare variables , When using variables, pay attention to using the variable name of the corresponding field （ That is to use V_EMP. Field name To call ）, If you do not use this form to call or omit to write oneortwo characters, an error will be reported ;

eg： use %TYPE Declare variable type , The printed job number is 7698 The job of , name Department number ;

DECLARE 
  V_EMPNO EMP.EMPNO%TYPE := 7698;
	V_ENAME EMP.ENAME%TYPE;
	V_DEPTNO EMP.DEPTNO%TYPE;
	
BEGIN
  	SELECT E.ENAME
		       ,E.DEPTNO
		INTO   V_ENAME
		       ,V_DEPTNO
		FROM EMP E
		WHERE E.EMPNO = V_EMPNO;
		
		DBMS_OUTPUT.put_line(V_ENAME);
    DBMS_OUTPUT.put_line(V_DEPTNO);
END;

eg： use %ROWTYPE Declare variable type , The printed job number is 7698 The job of , name Department number ;

DECLARE 
  V_EMP EMP%ROWTYPE;

BEGIN
	V_EMP.EMPNO := 7698;
	
	SELECT E.JOB
	       ,E.ENAME
				 ,E.DEPTNO
	INTO   V_EMP.JOB
	       ,V_EMP.ENAME
				 ,V_EMP.DEPTNO
	FROM EMP E
	WHERE V_EMP.EMPNO = E.EMPNO;
	
	DBMS_OUTPUT.put_line(V_EMP.JOB);
  DBMS_OUTPUT.put_line(V_EMP.ENAME);
	DBMS_OUTPUT.put_line(V_EMP.DEPTNO);
	
END;

c. Constant （CONSTANT）

Constants are given initial values when declared , No changes can be made throughout the life cycle ;

• Use... When using CONSTANT Keyword declaration constant ;

eg： Calculate the area of a circle ;

DECLARE
  PI   CONSTANT NUMBER := 3.14; -- PI length value  ①
  R    NUMBER := 3; -- The default value for the radius of a circle is 3 ② 
  --R NUMBER := 3; 
  AREA NUMBER; -- area .

BEGIN
  R := 5;
  AREA := PI * R * R; -- Calculated area  78.5
  DBMS_OUTPUT.PUT_LINE(AREA); -- The area of the output circle  78.5
  
  R := 6;
  AREA := PI * R * R; -- Calculated area  113.04
  DBMS_OUTPUT.PUT_LINE(AREA); -- The area of the output circle 
END;