Pl/sql basic syntax

1. Process oriented language

Print hello word

declare 
    --  The explanatory part （ Variable , Cursor or exception ）
   begin
      -- Procedural body 
      dbms_output.put_line("Hello Word");
   end;
   / -- Exit the compilation environment , And execute this program 
   
   
   -- Turn on the output switch 
   set serveroutput on
   / -- perform 
   
   ------ Output results -------
   Hello World
   
   
   -- Look at the structure of the package 
   desc dbms_output

​

Official grammar document

database-pl-sql-language-reference.pdf

Package related documentation

database-pl-sql-packages-and-types-reference.pdf

Define basic variables

type ：char,varchar2,date,number,boolean,long

give an example ： var1 char(15);

​ married boolean := true;

​ psal number(7,2);

Referential variables

​ pename emp.ename%type ; --pename The variable type will change with emp In the table ename The type of field changes

​ Be similar to pename varchar2(64);

Recordable variables

​ Be careful ： Represents a line of records , There are different types in a row of records

​ emp_rec emp%rowtype;

​ select * into emp_rec from emp where empno= 7839;

if Use of statements

The first type

​

IF  Conditions  THEN  sentence 1;
    sentence 2;
END IF;

The second type

IF  Conditions  THEN  sentence 1;
  
  ELSE  sentence 2;
  
END IF;

The third type

IF  Conditions  THEN  sentence ;
  ELSIF  sentence  THEN  sentence ;
  ELSE  sentence ;
END IF;

Enter a number from the keyboard

Loop statement

The first type

While total <= 25000 Loop
.....
total := total+salary;

END LOOP;

The second type

Loop
EXIT[when  Conditions ];
......
End loop;

The third type

FOR I IN 1...3 LOOp
 Statement sequence ;

END LOOP;

cursor ( amount to Java Result set Resultset)

Properties of the cursor

%fund %notfund Judge whether the cursor gets a record

%isopen: Determine whether the cursor is on

%rowcount Number of rows affected

CURSOR Light label [( Parameter name data type [, Parameter name data type ]…)] IS SELECT sentence ;

for example cursor c1 is select ename from emp;

Limit on the number of cursors

By default ,oracle The database can only be in the same session , open 300 Cursors

Query parameters

Modify the number of cursors

alter  system set open_cursors=400 scope=both;

Open the cursor ：

open c1; Open the cursor to execute the query

Close the cursor :

close c1; Close the cursor to free resources

Take the value of a row of cursors ：

fetch c1 into pename; Take a line into the variable

fetch The role of ：

1） Returns the record that the current pointer points to

2） Point the pointer to the next record

The use of the cursor

1. Define a cursor cursor cname is select …

1. Define a variable for the cursor pename emp.ename%type ; ( Reference type variable )
2. Open the cursor open cname
3. Take a record fetch cname intopename
4. Close the cursor close cname

set serveroutput ondeclare--  Define a cursor cursor  cemp is select ename,sal from emp;-- Define a cursor with parameters cursor cemp(dno number) is select ename from emp where deptno = dno;-- Define relative variables for the cursor pename emp.ename%type;psal emp.sal%type;begin -- Open cursor open cemp; loop   -- Take a record    fectch cemp into pename,psal;      exit when cemp%notfound;     --  Print   dbms_output.putline(pename || ' New water volume '|| psal);    end loop;      -- Close the cursor   close cemp;  end;  /

Be careful ： If PL/SQL The data is modified in , Remember that commit ;

​ about Oracle , The default transaction isolation level is read commiteed ;

abnormal

Throw exceptions

declare     The explanatory part ( Variable description 、 The cursor States 、 Exceptions )begin      Statement sequence exception     Exception handling statements end;/ give an example ：exception   when no_data_fund then dbms_output.put_line(" The employee was not found ");  when others then dbms_output.put_line(' Other exceptions ');end;/

Common abnormal

no_data_fund No data found

too_many_rows Returns multiple lines of data

zero_divide : 0 Can't do divisor

value_error: Arithmetic or conversion error , For example, a variable of string type is converted into a numeric variable .

Custom exception

When an exception is thrown and the cursor is not closed normally ,Oracle It will start automatically pmon process (Process Monitor) Will automatically recycle garbage process , It's kind of like Java Medium GC

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