PostgreSQL Oracle 兼容性之 - DBMS_SQL(存储过程动态SQL中使用绑定变量-DB端prepare statement)

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背景

Oracle中有一个dbms_sql的包,可以让你在存储过程的动态SQL中使用prepared statement。如果动态SQL的调用频次较高,硬解析可能导致一些性能问题(Oracle硬解析的CPU消耗还是蛮大的)。

https://docs.oracle.com/cd/B19306_01/appdev.102/b14258/d_sql.htm#i1028953

DMBS_SQL里面包含的一些类型

Bulk SQL Types  
  
BFILE_TABLE  
  
BINARY_DOUBLE_TABLE  
  
BLOB_TABLE  
  
CLOB_TABLE  
  
DATE_TABLE  
  
INTERVAL_DAY_TO_SECOND_TABLE  
  
INTERVAL_YEAR_TO_MONTH_TABLE  
  
NUMBER_TABLE  
  
TIME_TABLE  
  
TIME_WITH_TIME_ZONE_TABLE  
  
TIMESTAMP_TABLE  
  
TIMESTAMP_WITH_LTZ_TABLE  
  
UROWID_TABLE  
  
VARCHAR2_TABLE  

其中本文用到的 NUMBER_TABLE

TYPE number_table IS TABLE OF NUMBER INDEX BY BINARY_INTEGER;  

在PostgreSQL的INLINE CODE或者FUNCTION中如何使用动态SQL,如何使用绑定变量,如何使用BULK类型呢?

PostgreSQL INLINE CODE或函数的动态SQL、绑定变量使用

首先借这个链接,解释一下Oracle dbms_sql的使用

https://stackoverflow.com/questions/21335493/can-somebody-explain-dbms-sql-number-table

Better to understand DBMS_SQL itself to some extent, before understanding NUMBER_TABLE.   
( I do this for My Learning!)  
  
NUMBER_TABLE  
is Actually,  
  
TYPE number_table IS TABLE OF NUMBER INDEX BY BINARY_INTEGER;  
So, only numbers are allowed!  
  
FlowChart on How DBMS_SQL Works! :  
  
Your interested area comes in bind variable box  
                        -----------  
--                    | open_cursor |  
--                      -----------  
--                           |  
--                           |  
--                           v  
--                         -----  
--          ------------>| parse |  
--          |              -----  
--          |                |  
--          |                | ---------  
--          |                v          |  
--          |           --------------  |  
--          |-------->| bind_variable | |  
--          |     ^     -------------   |  
--          |     |           |         |  
--          |      -----------|         |  
--          |                 |<--------  
--          |                 v  
--          |               query?---------- yes ---------  
--          |                 |                           |  
--          |                no                           |  
--          |                 |                           |  
--          |                 v                           v  
--          |              -------                  -------------  
--          |----------->| execute |            ->| define_column |  
--          |              -------             |    -------------  
--          |                 |------------    |          |  
--          |                 |            |    ----------|  
--          |                 v            |              v  
--          |           --------------     |           -------  
--          |       ->| variable_value |   |  ------>| execute |  
--          |      |    --------------     | |         -------  
--          |      |          |            | |            |  
--          |       ----------|            | |            |  
--          |                 |            | |            v  
--          |                 |            | |        ----------  
--          |                 |<-----------  |----->| fetch_rows |  
--          |                 |              |        ----------  
--          |                 |              |            |  
--          |                 |              |            v  
--          |                 |              |  -----------------  
--          |                 |              | | column_value    |  
--          |                 |              | | variable_value  |  
--          |                 |              |  -----------------  
--          |                 |              |            |  
--          |                 |<--------------------------  
--          |                 |  
--           -----------------|  
--                            |  
--                            v  
--                       ------------  
--                     | close_cursor |  
--                       ------------  

例子

Example: In a DELETE statement, for example, you could bind in an array in the WHERE clause and have the statement be run for each element in the array:  
  
DECLARE  
  stmt VARCHAR2(200);  
  dept_no_array DBMS_SQL.NUMBER_TABLE;  
  c NUMBER;  
  dummy NUMBER;  
begin  
  dept_no_array(1) := 10; dept_no_array(2) := 20; /* Put some values into the array */  
  dept_no_array(3) := 30; dept_no_array(4) := 40;  
  dept_no_array(5) := 30; dept_no_array(6) := 40;  
  stmt := 'delete from emp where deptno = :dept_array'; /* A Dynamic SQL String with a bind variable */  
  c := DBMS_SQL.OPEN_CURSOR; /* Open a Cursor! */  
  DBMS_SQL.PARSE(c, stmt, DBMS_SQL.NATIVE); /* Parse the Dynamic SQL , making it happen on the native database to which is connected! */  
  
  DBMS_SQL.BIND_ARRAY(c, ':dept_array', dept_no_array, 1, 4);  
  /* Bind only elements 1 through 4 to the cursor Happens 4 times */  
  
  dummy := DBMS_SQL.EXECUTE(c);  
  /* Execute the Query, and return number of rows deleted! */  
  
  DBMS_SQL.CLOSE_CURSOR(c);   
  
  EXCEPTION WHEN OTHERS THEN  
    IF DBMS_SQL.IS_OPEN(c) THEN  
      DBMS_SQL.CLOSE_CURSOR(c);  
    END IF;  
    RAISE;  
END;  
/   
  
P.S. Pure rip-off, with some more commments ,from Oracle  

PostgreSQL 服务端绑定变量的用法与之类似

PREPARE,准备DB端绑定变量SQL

EXECUTE,绑定并执行

DEALLOCATE,删除绑定变量

详见:

https://www.postgresql.org/docs/devel/static/sql-prepare.html

因此以上Oracle的代码可以改成如下:

do language plpgsql $$  
DECLARE  
  stmt VARCHAR(200);  
  dept_no_array numeric[];  
  c numeric;  
begin  
  dept_no_array[1] := 10; dept_no_array[2] := 20; /* Put some values into the array */  
  dept_no_array[3] := 30; dept_no_array[4] := 40;  
  dept_no_array[5] := 30; dept_no_array[6] := 40;  
  execute format('prepare stmt(numeric) as delete from emp where deptno = $1');    /* A Dynamic SQL String with a bind variable */  
  
  foreach c in array dept_no_array[1:4]  
  loop  
    execute format('execute stmt(%s)', c);   -- 执行绑定SQL  
  end loop;  
  
  DEALLOCATE stmt;  
  
  EXCEPTION WHEN OTHERS THEN  
    DEALLOCATE stmt;  
    RAISE;  
END;  
$$;  

如果不需要用到绑定变量,那就更简单了。

do language plpgsql $$  
DECLARE  
  dept_no_array numeric[];  
  c numeric;  
begin  
  dept_no_array[1] := 10; dept_no_array[2] := 20; /* Put some values into the array */  
  dept_no_array[3] := 30; dept_no_array[4] := 40;  
  dept_no_array[5] := 30; dept_no_array[6] := 40;  
  
  foreach c in array dept_no_array[1:4]  
  loop  
    delete from emp where deptno = c;  
  end loop;  
  
  DEALLOCATE stmt;  
  
  EXCEPTION WHEN OTHERS THEN  
    DEALLOCATE stmt;  
    RAISE;  
END;  
$$;  

例子

建表

do language plpgsql $$
declare
begin
  execute 'drop table if exists test';
  execute 'create table test(id int primary key, info text, crt_time timestamp)';
  
  for i in 0..1023 loop
    execute format('drop table if exists test%s', i);
    execute format('create table test%s (like test including all)', i);
  end loop;
end;
$$;

使用动态SQL,写入目标子表

create or replace function dyn_pre(int) returns void as $$
declare
  suffix int := mod($1,1024);
begin
  execute format('insert into test%s values(%s, md5(random()::text), now()) on conflict(id) do update set info=excluded.info,crt_time=excluded.crt_time', suffix, $1);
end;
$$ language plpgsql strict;

使用绑定变量,写入目标子表

create or replace function dyn_pre(int) returns void as $$
declare
  suffix int := mod($1,1024);
begin
  execute format('execute p%s(%s)', suffix, $1);
  exception when others then
    execute format('prepare p%s(int) as insert into test%s values($1, md5(random()::text), now()) on conflict(id) do update set info=excluded.info,crt_time=excluded.crt_time', suffix, suffix);
    execute format('execute p%s(%s)', suffix, $1);
end;
$$ language plpgsql strict;

性能对比

vi test.sql

\set id random(1,1000000000)
select dyn_pre(:id);

pgbench -M prepared -n -r -P 1 -f ./test.sql -c 56 -j 56 -T 120

1、使用动态SQL,TPS约5.2万。

2、使用函数内绑定变量,TPS约13.4万。

参考

https://www.postgresql.org/docs/devel/static/sql-prepare.html

https://stackoverflow.com/questions/21335493/can-somebody-explain-dbms-sql-number-table

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