Oracle PL / SQL programming

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One 、 summary

PL/SQL Is in sql On the basis of , It's to deal with sql Some complex business logic processing that cannot be carried out .

1、 Program structure

A complete PL/SQL Statement blocks generally have 3 Component composition .
1： Declaration part （declare）
2： Executive part （begin）
3： Exception handling part （exception）

declare
	 Declaration part 
  begin
     Executive part 
  exception
     Exception handling part 
  end

Two 、 Constant

1、 Basic data type

1： value type
number,number(x,y),x Is the significant bit ,y It's a decimal place , for example number(5,2) Indicates that the definition of a significant bit is 5 position , The decimal places are 2 Of .
2： Character type
varchar2,char
varchar2 Used to store variable length strings ,char Type is used to store strings of a specified length .
3： The date type
date,timestamp
data Type stores date and time information ,timestamp Store in data similar , But it also includes the decimal part of the second
4： Boolean type
boolean
5：lob type
blob,clob,nclob,bfile
clob,nclob Store text data ,blob Store binary data ,bfile Store pointers to operating system files .

2、 Special data types

In addition to the basic data types above ,PL/SQL It also provides 3 A special data type , this 3 All data types are based on basic data types .

The syntax is as follows

type myrecord is record(
field1 datatype [not null][:=default value]
)

Define a record type myrecord, Used to store student Students' names and class names in the table

declare
	type myrecord is record
	my_name varchar2<20>,
	my_class varchar2<20>;
	Myrecord myrecord;
	begin
		select name,class into myrecord from student where id = 1;
		dbms_output.put_line<' The student name inquired is ：' || Myrecord.my_name ||', His class is ：‘|| Myrecord.my_class >;
	end;	

3、%type type

stay oracle We often use the data types of fields in , When we define a data type to be consistent with the existing field types in the table, we can use %type type , For example, we declare a relation with student In the table name The field types are consistent var_name

var_name student.name%type

4、%rowtype type

You can tell by the name rowtype Represents all data types of a row in the data table , So you can record a row of data after using it . For example, declare a for storing student Variables recorded in each row of the table var_row

var_row student %rowtype

Declare one for storing student In the table id=1 One line of records var_row, And display basic information

declare
	var_row student%rowtype;
begin
	select * into var_row from student where id =1;	
	dbms_output.put_like<' The student name inquired is ：' || var_row.name>
end;

5、 Record form type

The types we mentioned above can only store one data , Or a row of data , Cannot store multiple rows of data , Now we need to store multiple rows of data . The grammar is as follows

type  Record table type name  is table of  type  index by binary_integer

Define a record table type to store student Table data , And display

declare
	type mytabletype is table of student%rowtype index by binary_integer;
	Mytable mytabletype;
begin
	select * into mytable<1> from student where id = 1;
	select * into mytable<2> from student where id = 2;
	dbms_output.put_line<' The student's name is ：'|| mytable<1>.name>;
	dbms_output.put_line<' The student's name is ：'|| mytable<2>.name>;
end;	

3、 ... and 、 Variable

1、 Definition of variables

We must first define variables in the declaration section , Not familiar with other programming languages ,PL/SQL Language requires variable names to be in front , The data type is later , The syntax for defining variables is as follows .

 Variable name   data type  [ The default value is  |: =  Initial value ]

For example, the following code

var_name varchar2(20):=' Zhang San '

2、 The assignment of a variable

1： Direct assignment

name:=' Zhang San ';
age:=age+10;

2： Interactive assignment

name:=&temp;

Running this code will prompt for temp Value , Then assign the input value to name Variable

3： Use select In the query statement into Clause

select name into name_temp from student where id = 1;

3、 Scope of variable

Scope of variable , In a normal PL/SQL Fast mid , The scope of variables starts from the declaration , Until the end of the block . If there is block nesting , Then the externally declared is a global variable , It can be used externally or internally .

Four 、 Definition of constant

1、 Constant

The value of the constant remains unchanged during the running of the program , Constants are declared in a way similar to variables , But include keywords constant, When defining constants, initial values should be given , As shown below .

pi constant number:=3.1415;

5、 ... and 、 Conditional statements

if
case

1、if sentence

There are three forms ：if…then sentence 、if…then…else Statement and if…then…elsif sentence .

1、if…then sentence

The basic syntax is as follows

if  Conditional expression  then
 Statement sequence ;
end if;

When the result of the conditional expression is true when , The program runs then The following statement sequence , If false when , Then skip then Run the following end if Subsequent statements .

2、if…then…else sentence

The basic syntax is as follows

if  Conditional expression  then
 Statement sequence 1;
else
 Statement sequence 2;
end if;

When the result of the conditional expression is true when , Program running statement sequence 1, If false when , Run the statement sequence 2.

3、if…then…elseif sentence

The basic syntax is as follows

if  Conditional expression  1 then
 Statement sequence 1;
elseif  Conditional expression 2
 Statement sequence 2;
...
else
 Conditional expression n
end if;

When the result of the conditional expression is true when , Program running statement sequence 1, If false when , Run the statement sequence 2.

2、case sentence

The grammar is as follows

case  Selector expressions 
	when  Conditions  1 then  Statement sequence  1;
	when  Conditions  2 then  Statement sequence  2;
	...
	when  Conditions  n then  Statement sequence  n;
	else  Statement sequence  n+1;
	end case;

6、 ... and 、 Loop statement

loop
while
for

1、loop loop

This kind of circulation includes the circulation conditions in the circulation body ,loop The loop will first execute the loop body , Then judge whether the set conditions are met to determine whether the cycle continues . The syntax is as follows

loop
 Statement sequence ;
exit when  Conditional expression 
end loop

First execute the statement sequence , Then judge the next operation according to the value of the conditional expression , If the value of the conditional expression is true, Then exit the loop , If the value of the conditional expression is false, Then continue to execute the loop body .

2、while loop

while Loop is to judge the condition first , If the condition is true, execute the loop body , If not , Just exit the loop , The syntax is as follows .

while  Conditional expression  loop
 Statement sequence ;
end loop;

When it's running , First, judge the conditional expression , If it turns out to be true, Then run the statement sequence in the loop body , If false, Then exit the loop .

3、for loop

The number of cycles in the first two cycles depends on whether the condition is true ,for The cycle can define the number of cycles by itself . The syntax is as follows

for  Loop variable  in [reverse]  Start number ... End value  loop
 Statement sequence ;
end loop;

When the loop variable is greater than the starting value , When it is less than the end value , Execute a sequence of statements , Otherwise exit the loop , By default, loop variables are incremented in a loop , If used reverse Parameters , Then the cycle decreases .

7、 ... and 、 exception handling

A complete PL/SQL Statement blocks generally have 3 Component composition , Among them the first 3 The second part is the exception handling part ,oracle Provides exceptions （exception） And exception handling （exception handler） To achieve error handling . An error corresponds to an exception , When something goes wrong , The exception handler will catch the corresponding exception , The exception handler handles runtime errors .

1、 The kind of anomaly

oracle Runtime errors can be divided into oracle Errors and user defined errors , Corresponding to this , According to the mechanism and principle of exception generation , Can be Oracle The system exceptions of are divided into 3 Kind of .
1： Predefined exceptions ： Corresponding to oracle error , yes Oracle Provided by the system itself , Users can go to PL/SQL The exception handling section represents them by name . Handling of these exceptions , Users do not need to define , By oracle Automatic triggering .
2： Non predefined exception ： Other standards oracle error , How to deal with this abnormal situation , The user is required to define , Then from oracle Automatically trigger it .
3： User defined exception ： Program execution , There is something abnormal that the programmer thinks . The handling of this exception requires the user to define , Then the displayed will trigger it in the program .

2、 Exception handling

1、 Exception definition

 Abnormal variable  excption

If it is a non predefined exception , You also need to associate this exception variable with the error number , The grammar is as follows

prama excption_int( Abnormal variable ,-#####)

among ,“#####” by oracle Error number of

2、 Exception correlation

In the execution part, when an error occurs, the exception corresponding to the error is associated , Because the system can automatically identify oracle internal error , Therefore, when an error occurs, the system will automatically associate the corresponding predefined exception or non predefined exception , But user-defined errors , The system cannot automatically recognize , User programming is required for Correlation , The associated syntax is as follows .

raise user_define_recption

3、 Exception catching and handling

When an error occurs , In the exception handling part, the exception is caught and handled by the exception handler . The grammar is as follows .

exception
when  abnormal  1 [OR abnormal ......]then  Process sequence statements  1;
when  abnormal  2 [OR abnormal ......]then  Process sequence statements  2;
...
when  abnormal  n [OR abnormal ......]then  Process sequence statements  n;
end;

An exception can only be caught by an exception handler , And process it
A processor can catch multiple exceptions , At this point through OR Connect

3、 Exception handling instance

Inquire about student In the table name by “ Zhang San ” Student information , If there is no such student , The output “ No data record returned ”, If there are multiple records , The output “ Return data record exceeds one line ”.

declare
	var_name student.name%type;
begin
	select name into var_name from student where name = ' Zhang San ';
	if sql%found then 		-- If it's a line , It shows the results 
		dbms_output.put_line<' The student's name ：' || var_name>;
	end if;
exception
	when too_many_rows then	-- Capture exception 
		dbms_output.put_line<' Return data record exceeds one line '>;
	when no_data_found then
		dbms_output.put_line<' No data record returned '>;
	end;

8、 ... and 、 summary

The relevant contents here have not been sorted out yet , The article continues to be updated later , Recommended collection .

The commands involved in the article must be typed several times each like me , Only in the process of knocking can you find out whether you really master the command .

You can search by wechat 【 Xiaoqi JAVA interview 】 First time reading , reply 【 Information 】 Access to benefits , reply 【 project 】 Get the source code of the project , reply 【 The resume template 】 Get resume template , reply 【 Learning Roadmap 】 Get a learning roadmap .