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PG basics -- Logical Structure Management (trigger)

2022-07-01 12:53:00 【51CTO】

Create trigger

1） First, create an execution function for the trigger , The return type of this function is trigger type

2） Build a trigger

       
       postgres
       
       =# 
       
       create function student_delete_trigger
       
       (
       
       )
       
postgres
       
       -# returns trigger 
       
       as $$
       
postgres$# 
       
       begin
       
postgres$# 
       
       delete 
       
       from score 
       
       where student_no
       
       =OLD
       
       .student_no
       
       ;
       
postgres$#  return OLD
       
       ;
       
postgres$# end
       
       ;
       
postgres$# $$
       
postgres
       
       -# language plpgsql
       
       ;
       
       CREATE FUNCTION
       
postgres
       
       =# 
       
postgres
       
       =# 
       
       create trigger delete_student_trigger
       
postgres
       
       -# after 
       
       delete 
       
       on student
       
postgres
       
       -# for each row execute procedure student_delete_trigger
       
       (
       
       )
       
       ;
       
       CREATE TRIGGER
       
postgres
       
       =# 
       
       insert 
       
       into student 
       
       values
       
       (
       
       1
       
       ,
       
       ' Zhang San '
       
       ,
       
       14
       
       )
       
       ;
       
       insert 
       
       into student 
       
       values
       
       (
       
       2
       
       ,
       
       ' Li Si '
       
       ,
       
       14
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       1
       
postgres
       
       =# 
       
       insert 
       
       into student 
       
       values
       
       (
       
       2
       
       ,
       
       ' Li Si '
       
       ,
       
       14
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       1
       
postgres
       
       =# 
       
       insert 
       
       into student 
       
       values
       
       (
       
       3
       
       ,
       
       ' The king 2 '
       
       ,
       
       14
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       1
       
postgres
       
       =# 
       
postgres
       
       =# 
       
       insert 
       
       into score 
       
       values
       
       (
       
       1
       
       ,
       
       85
       
       ,
       
       75
       
       ,
       
       date '2022-06-29'
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       1
       
postgres
       
       =# 
       
       insert 
       
       into score 
       
       values
       
       (
       
       1
       
       ,
       
       80
       
       ,
       
       73
       
       ,
       
       date '2022-01-29'
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       1
       
postgres
       
       =# 
       
       insert 
       
       into score 
       
       values
       
       (
       
       2
       
       ,
       
       87
       
       ,
       
       75
       
       ,
       
       date '2022-03-29'
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       1
       
postgres
       
       =# 
       
       insert 
       
       into score 
       
       values
       
       (
       
       3
       
       ,
       
       75
       
       ,
       
       75
       
       ,
       
       date '2022-06-29'
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       1
       
postgres
       
       =# 
       
       insert 
       
       into score 
       
       values
       
       (
       
       3
       
       ,
       
       55
       
       ,
       
       75
       
       ,
       
       date '2022-04-29'
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       1
       
postgres
       
       =# 
       
       delete 
       
       from student 
       
       where student_no
       
       =
       
       3
       
       ;
       
       DELETE 
       
       1
       
postgres
       
       =# 
       
       select 
       
       * 
       
       from score
       
       ;
       
 student_no 
       
       | chinese_score 
       
       | math_score 
       
       | test_date  
       
       ------------+---------------+------------+------------
       
       1 
       
       |            
       
       85 
       
       |         
       
       75 
       
       | 
       
       2022
       
       -
       
       06
       
       -
       
       29
       
       1 
       
       |            
       
       80 
       
       |         
       
       73 
       
       | 
       
       2022
       
       -
       
       01
       
       -
       
       29
       
       2 
       
       |            
       
       87 
       
       |         
       
       75 
       
       | 
       
       2022
       
       -
       
       03
       
       -
       
       29
       
       (
       
       3 rows
       
       )
      
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Statement level triggers

Statement level triggers refer to the execution of each sql Statement is executed only once .

       
       create 
       
       table log_student
       
       (
       
update_time 
       
       timestamp
       
       ,
       
db_user 
       
       varchar
       
       (
       
       40
       
       )
       
       ,
       
opr_type 
       
       varchar
       
       (
       
       6
       
       )  
       
       )
       
       create 
       
       or replace function log_student_trigger
       
       (
       
       )
       
returns trigger 
       
       as $$
       
       begin
       
       insert 
       
       into log_student 
       
       values 
       
       (now
       
       (
       
       )
       
       ,user
       
       ,TG_OP
       
       )
       
       ;
       
return 
       
       null
       
       ;
       
end
       
       ;
       
$$
       
language 
       
       "plpgsql"
       
       ;
       
TG_OP Is a special variable in the trigger function , representative DML Operation type 
       
       create trigger log_student_trigger
       
after 
       
       insert 
       
       or 
       
       delete 
       
       or 
       
       update 
       
       on student
       
for statement execute procedure log_student_trigger
       
       (
       
       )
       
       ;
      
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Although deleted 2 Bar record , But the execution is a statement , So in log_student Only one operation is recorded in .

       
       postgres
       
       =# 
       
       delete 
       
       from student
       
       ;
       
       DELETE 
       
       2
       
       ^
       
postgres
       
       =# 
       
       select 
       
       * 
       
       from log_student
       
       ;        
       
        update_time         
       
       | db_user  
       
       | opr_type 
       
       ----------------------------+----------+----------
       
       2022
       
       -
       
       06
       
       -
       
       30 
       
       10
       
       :
       
       26
       
       :
       
       48.847478 
       
       | postgres 
       
       | 
       
       DELETE
       
       (
       
       1 row
       
       )
      
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Line level triggers

Row level triggers execute each row SQL Statements are executed once

       
       drop trigger log_student_trigger 
       
       on student
       
       ;
       
       delete 
       
       from log_student
       
       ;
       
       delete 
       
       from student
       
       ;
      
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       create trigger log_student_trigger2 
       
   after 
       
       insert 
       
       or 
       
       delete 
       
       or 
       
       update 
       
       on student
       
   for ROW EXECUTE PROCEDURE log_student_trigger
       
       (
       
       )
       
       ;
       
postgres
       
       =# 
       
       insert 
       
       into student 
       
       values 
       
       (
       
       1
       
       ,
       
       ' Zhang San '
       
       ,
       
       14
       
       )
       
       ,
       
       (
       
       2
       
       ,
       
       ' Li Si '
       
       ,
       
       30
       
       )
       
       ;
       
       INSERT 
       
       0 
       
       2
       
postgres
       
       =# 
       
       select 
       
       * 
       
       from log_student
       
       ;
       
        update_time         
       
       | db_user  
       
       | opr_type 
       
       ----------------------------+----------+----------
       
       2022
       
       -
       
       06
       
       -
       
       30 
       
       10
       
       :
       
       42
       
       :
       
       58.834223 
       
       | postgres 
       
       | 
       
       INSERT
       
       2022
       
       -
       
       06
       
       -
       
       30 
       
       10
       
       :
       
       42
       
       :
       
       58.834223 
       
       | postgres 
       
       | 
       
       INSERT
       
       (
       
       2 rows
       
       )
      
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You can see a line sql Execution insert 2 Row data , The log table records 2 Bar record

BEFORE trigger

Statement level BEFOR Triggers are triggered before the statement starts doing anything

Line level BEFORE Triggers are triggered before the operation on a specific row .

AFTER trigger

Statement level AFTER Triggers are triggered at the end of the statement

Line level AFTER Triggers are triggered at the end of the statement , It will be at any statement level AFTER Trigger before trigger .

Delete trigger

       
       drop trigger 
       
       [if exists
       
       ] name 
       
       ON 
       
       table 
       
       [cascade 
       
       |restrict
       
       ]
       
       ;
      
1.

if exists If the trigger does not exist , Send out a notice Not a mistake

cascade Cascade delete objects that depend on this trigger

restrict If there are dependent objects, they refuse to delete

Be careful ： When you delete a trigger , The function of the trigger will not be deleted , however , When deleting a table , The trigger on the table will be deleted .

Trigger function has return value , Statement level triggers should always return NULL, That is, the required display is written in the trigger function return null, Otherwise, the report will be wrong .

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