Study notes 22/1/19 and 22/1/20

Learning notes

One 、 The cursor

（1） Cursor without parameters

Cursor declaration format ：

DECLARE
  CURSOR  You name    
  IS
  SELECT  sentence ;--- The result set of the query to which the cursor points 
BEGIN
  --  Open cursor   Logical body ( The use of cursors / perform   Put it here )
END;

The cursor automatically uses the format ：
eg： take EMP Employee job number of the table 、 Print out the name together ;

DECLARE 
  CURSOR C_EMP IS 
  SELECT EMPNO
        ,ENAME
  FROM EMP ;

BEGIN 
  FOR I IN C_EMP LOOP  --  Call cursor format 
     DBMS_OUTPUT.put_line(I.EMPNO||' '||I.ENAME);
  END LOOP;
END;

（2） Cursors with parameters

Declaration format ：

DECLARE
  CURSOR  You name  ( Parameters 1  data type  ,  Parameters 2  data type  .. .. )  
  IS
  SELECT  sentence ;--- The result set of the query to which the cursor points 
BEGIN
  --  Open cursor   Logical body ( The use of cursors / perform   Put it here )
END;

eg： Pass in a department number , Print out the names of the employees in this department ;

DECLARE 
  CURSOR C_EMP(P_DEPTNO NUMBER ) IS
  SELECT T.ENAME
  FROM EMP T 
  WHERE T.DEPTNO = P_DEPTNO ;
  
  V_DEPTNO NUMBER;
  V_JOB VARCHAR2(30);
BEGIN 
  V_DEPTNO:= & Enter the department number you want to print ;  

  FOR I IN C_EMP(V_DEPTNO) LOOP 
       DBMS_OUTPUT.put_line(I.ENAME);
  END LOOP;
END;

eg： Update according to business requirements EMP_0118 Pay for
Pass in a department number , Update the salary of employees in this department
1. If the employee's basic salary is lower than 1500, Just give this employee 1000 The basic salary of
2. If the employee's basic salary is higher than 1500, And the bonus is empty or equal to 0, Just give this employee 100 A dollar bonus

DECLARE 
  CURSOR C_EMP(P_DEPTNO NUMBER) IS
  SELECT T.EMPNO
        ,T.SAL
        ,T.COMM
  FROM EMP_0118 T 
  WHERE T.DEPTNO = P_DEPTNO;
  
  V_DEPTNO NUMBER;
BEGIN 
  V_DEPTNO := 10;
  
  FOR I IN C_EMP(V_DEPTNO) LOOP
     IF I.SAL <1500 THEN 
        UPDATE EMP_0118 T SET T.SAL = T.SAL + 1000
        WHERE T.EMPNO  = I.EMPNO;
     ELSIF I.SAL >= 1500 AND NVL(I.COMM,0) = 0 THEN 
        UPDATE EMP_0118 T SET T.COMM = 100
        WHERE T.EMPNO  = I.EMPNO;
     END IF;
  END LOOP;
  
  COMMIT;

END;

We need to pay attention to ：

1. The data type of the parameter should not have length , Just define the type ;
2. Parameters are defined , You have to pass parameters in ;
3. What data type is the defined parameter , When transferring parameters, you must transfer the value of the data type .

The difference between parameters and variables ：

1. Data type cannot be added to parameter declaration 【 length 】 , Variables need to be specified in length ;
2. Variable After the statement , It can be unassigned perhaps After the assignment It can also be done without , But the parameters
   Just make a statement , Must use .

I'm sorry for cursor This will be some of the views of ,cursor This would look to me like a pointer to a table that can store all types of tables , Point to the table we need , It feels like a function , But it's different , Later, I learned about stored procedures 、 After the functions and views, come back and summarize the differences between the four ！

Two 、 Character splicing and dynamic SQL

（1） Character splicing

This part is about mastering two things ：
- || Connector
- Various escape characters

First of all, we need to know what we need , In fact, strings and variables can be connected with connectors , I also learned to use when learning simple query statements || Connect the percent sign , Just know that it is a connector ;

Then there is the matter of escape characters , First , We know that oracle The part enclosed in single quotation marks is the data of a character type , But when I first started learning single quotation marks, I thought about how to use single quotation marks to represent a simple string , Is to output a string , There are actually two ways to do this ;
1. Escape character
First we need to know what the escape character means , seeing the name of a thing one thinks of its function , That is to say, the special meaning of the special symbol behind the symbol is converted to it , Make it output as a normal character , If you are interested in this aspect, you can take a look at the compilation principle ;

There are two kinds of escape characters

（2） dynamic SQL

1. Use dynamic SQL Perform simple DDL sentence ：
eg： Execute table creation statement ;

BEGIN 
  --CREATE TABLE EMP_0120 AS SELECT * FROM EMP;
  EXECUTE IMMEDIATE 'CREATE TABLE EMP_0120 AS SELECT * FROM EMP';
END;

eg： Execute delete statement ;

DECLARE 
 V_JOB VARCHAR2(20);
 V_SQL VARCHAR2(4000);
BEGIN 
  V_JOB := &INPUT_JOB;
  --DELETE FROM EMP_0103 T WHERE T.JOB = V_JOB;
   ----- Single quotation marks are special characters , Represents a single quotation mark in a string , You need two single quotation mark escapes to represent a single quotation mark 
  --chr(39)  It also means a single quotation mark 
  --V_SQL := 'DELETE FROM EMP_0103 T WHERE T.JOB ='||'''' ||V_JOB ||'''';
  V_SQL := 'DELETE FROM EMP_0120 T WHERE T.JOB =' ||CHR(39)||V_JOB||CHR(39);
  
  DBMS_OUTPUT.put_line(V_SQL);
  EXECUTE IMMEDIATE V_SQL;
  --COMMIT;
END;

2. Parameterized SQL sentence

• If the dynamic statement is SELECT sentence , You can save the query results to INTO In the following variables .
  If there are parameters in the dynamic statement ,USING Pass values for parameters in the statement .
  dynamic SQL The parameter format in is : Parameter name , Parameters need to be used at run time USING Pass value .

eg： Based on the incoming empno and deptno Find out the name and salary of the corresponding employee ;

• Directly in the program block select sentence

DECLARE 
  V_SQL VARCHAR2(4000);
  V_ENAME VARCHAR2(40);
  V_SAL NUMBER;
  V_EMPNO NUMBER;
  V_DEPTNO NUMBER;
BEGIN 
  V_EMPNO :=&INPUT_EMPNO; 
  V_DEPTNO := &INPUT_DEPTNO;
  
 SELECT T.ENAME
          ,T.SAL
  INTO V_ENAME
       ,V_SAL
  FROM EMP T 
  WHERE T.EMPNO = V_EMPNO
    AND T.DEPTNO = V_DEPTNO;
  DBMS_OUTPUT.put_line(V_ENAME ||' '|| V_SAL);
END;

• Use dynamic with parameters SQL sentence

DECLARE 
  V_SQL VARCHAR2(4000);
  V_ENAME VARCHAR2(40);
  V_SAL NUMBER;
  V_EMPNO NUMBER;
  V_DEPTNO NUMBER;
BEGIN 
  V_EMPNO :=&INPUT_EMPNO; 
  V_DEPTNO := &INPUT_DEPTNO;
  
    V_SQL := 'SELECT T.ENAME ,T.SAL FROM EMP T WHERE T.EMPNO = :P_EMPNO AND T.DEPTNO = :P_DEPTNO'; ----  use  : Parameter name  
           
  EXECUTE IMMEDIATE  V_SQL
   INTO V_ENAME  --- dynamic SQL The data found should be given to variables 
       ,V_SAL
   USING V_EMPNO,V_DEPTNO; --- Pay attention to the order of parameters 
   -- Put the variable  V_EMPNO  Pass to dynamic  SQL  Parameters of P_EMPNO
   
 DBMS_OUTPUT.put_line(V_ENAME ||' '|| V_SAL);  
   
END; 

eg： Pass in a job number with dynamic parameters SQL Methods Or use String concatenated without parameters Put this job number The employee's name and salary can be found out , Print name and salary on the output window ;

• With parameters SQL

DECLARE 
    V_SQL VARCHAR(3000);
    V_ENO NUMBER;
    V_EN VARCHAR2(20);
    V_SAL NUMBER;

BEGIN
    V_ENO := &INPUT_EMPNO;
    V_SQL := 'SELECT ENAME ,SAL FROM EMP WHERE EMPNO = : P_EMPNO ';
              
    EXECUTE IMMEDIATE V_SQL
                 INTO V_EN
                      ,V_SAL
                 USING V_ENO;
    COMMIT;
     
    DBMS_OUTPUT.put_line(V_EN||' '||V_SAL);

END;

• Splicing without parameters

DECLARE 
    V_SQL VARCHAR2(3000);
    V_ENO NUMBER := &INPUT_EMPNO;
    V_EN VARCHAR2(10);
    V_SAL NUMBER;  

BEGIN
    V_SQL := ' SELECT ENAME ,SAL FROM EMP WHERE EMPNO = '||V_ENO;
    

    EXECUTE IMMEDIATE V_SQL
                 INTO V_EN
                      ,V_SAL;
    
    DBMS_OUTPUT.put_line(V_EN||' '||V_SAL);

END;

3、 ... and 、 recursive

It's too late today , The following is a supplement to the story