POSTGRESQL 存储过程实战

CREATE TABLE department(
   ID INT PRIMARY KEY                         NOT NULL,
   d_code                                     VARCHAR(50),
   d_name                                     VARCHAR(50)     NOT NULL,
   d_parentID                                 INT             NOT NULL  DEFAULT 0
); 
--insert into department values(1,‘001‘,‘office‘);
--insert into department values(2,‘002‘,‘office‘,1);

drop function f_getNewID(text,text);
create or replace function f_getNewID(myTableName text,myFeildName text) returns integer as $$
declare
    mysql text;
        myID integer;
begin
    mysql:=‘select max( $1 ) from $2‘;
        execute mysql into myID using myFeildName,myTableName; 
    
    if myID is null or myID=0 then return 1;
    else return myID+1;
      end if;
end;
$$ language plpgsql;

--大家可以试一下，上面这个是会报错的
--select f_getNewID(‘department‘,‘ID‘);
--出错！

EXECUTE ‘SELECT count(*) FROM mytable WHERE inserted_by = $1 AND inserted <= $2‘
   INTO c
   USING checked_user, checked_date;

--这个看了？
---------------------------------------
EXECUTE ‘SELECT count(*) FROM ‘
    || quote_ident(tabname)
    || ‘ WHERE inserted_by = $1 AND inserted <= $2‘
   INTO c
   USING checked_user, checked_date;

--这个看了？
---------------------------------------
EXECUTE ‘UPDATE tbl SET ‘
        || quote_ident(colname)
        || ‘ = ‘
        || quote_literal(newvalue)
        || ‘ WHERE key = ‘
        || quote_literal(keyvalue);

--=============================
--好吧， 我改
------------------------------------------------------
drop function f_getNewID(text,text);
create or replace function f_getNewID(myTableName text,myFeildName text) returns integer as $$
declare
    mysql text;
    myID integer;
begin
    mysql:=‘select max(‘
        || quote_ident(myFeildName) 
        ||‘) from ‘
        || quote_ident(myTableName);
    execute mysql into myID; 
    --using myTableName,myFeildName;
    
    if myID is null or myID=0 then return 1;
    else return myID+1;
      end if;
end;
$$ language plpgsql;

--==============================
--漂亮，成功了！
--But Why?
--注意 对象（表名、字段名等）是不可以直接用变量的，要用  quote_ident()
-------------------------------------------------------
postgres=# select f_getnewid(‘department‘,‘ID‘);
--错误:  字段 "ID" 不存在
--第1行select max("ID") from department
                ^
--查询:  select max("ID") from department
--背景:  在EXECUTE的第10行的PL/pgSQL函数f_getnewid(text,text)

--===============================
--什么情况，ID怎么会有双引号，引号，号，号？？？
----------------------------------------------------------
--这里要感谢大神：权宗亮@飞象数据
--改成这样：

postgres=# select f_getnewid(‘department‘,‘id‘);
 f_getnewid
------------
          2
(1 行记录)

----终于成功了！大小写还有区别吗？？？ --but why? --当在命令行输入

CREATE TABLE role(
   ID                                         INT PRIMARY KEY NOT NULL,
   r_name                                     VARCHAR(50)     NOT NULL,
   r_paretnID                                 INT             NOT NULL    DEFAULT 0  
);

--结果在pgAdmin里看到的却是小写的

--同样，如果是在QUERY TOOLS 下用这样的语句创建还是 所有的字体名为小写
--如果我就想大写怎么办？？？？
--要这样写

CREATE TABLE "RoleUPER"(
   "ID"                                         INT PRIMARY KEY NOT NULL,
   r_name                                     VARCHAR(50)     NOT NULL,
   "r_paretnID"                                 INT             NOT NULL    DEFAULT 0  
);

--再用大象看看

--可以了！ 

create or replace function f_getNewID(myTableName text,myFeildName text) returns integer as $$
declare
    mysql text;
        myID integer;
begin
    mysql:=‘select max(‘|| $2 || ‘ ) from ‘||$1;
        execute mysql into myID using myFeildName,myTableName; 
    if myID is null or myID=0 then return 1;
    else return myID+1;
      end if;
end;
$$ language plpgsql;