Question

我正在尝试创建一个函数，该函数对所有一个查询值的结果进行求和，并将其与另一个简单查询进行比较。

这就是我所拥有的，但是我在开始（第二行）附近遇到语法错误：

CREATE FUNCTION trigf1(sbno integer, scid numeric(4,0)) RETURNS integer
BEGIN
    declare sum int default 0;
    declare max as SELECT totvoters FROM ballotbox WHERE cid=scid AND bno=sbno;

    for r as
        SELECT nofvotes FROM votes WHERE cid=scid AND bno=sbno;
    do
        set sum = sum + r.nofvotes;
    end for

    if sum > max
        then return(0);
    else
        return(1);
END

这导致：

'BEGIN'附近的语法错误

我正在使用postgreSQL和pgadminIII（以防它是相关的）。

我不知道为什么我会收到这个错误，所有内容似乎都与教科书定义完全一样。（这是我正在使用的教科书：http://digilib.usu.ac.id/buku/107859/Database-systems-concepts,-6th-ed.html）

Answer 1

我不知道哪本＆＃34;教科书＆＃34;你正在使用，但如果你写的所有内容与那本书完全一样，那本书就完全错了：

CREATE FUNCTION trigf1(sbno integer, scid numeric(4,0)) 
    RETURNS integer
AS         -- error #1: no AS keyword
$body$     -- error #2: use dollar quoting to specify the function body as a string
DECLARE    -- error #3: the declare block comes before the actual code
   sum_ integer := 0; -- error #5: you can't use a reserved keyword as a variable
   max_ integer;      -- error #6:  you can't initialize a variable with a select,
   r   record;   -- you need to declare the record for the cursor loop
BEGIN
   select totvoters
     into max_
   from ballotbox 
   WHERE cid=scid AND bno=sbno;

    -- error #7: the syntax for a loop uses IN not AS
    -- error #8: you need to declare R before you can use it
    -- error #9: the SELECT for a cursor loop must NOT be terminated with a ;
    FOR r IN SELECT nofvotes FROM votes WHERE cid=scid AND bno=sbno
    loop  -- error #10: you need to use LOOP, not DO

        sum_ := sum_ + r.nofvotes;  -- error #11: you need to use := for an assignment, not SET
    end loop; -- error #12: it's END LOOP
              -- error #13: you need to terminate the statement with a ;

    if sum_ > max_ then 
       return 0;
    else
       return 1;
    end if; -- error #14: an END if is required
END;
$body$
language plpgsql; -- error #14: you need to specify the language

手册记录了所有这些：

错误＃1，＃2：http://www.postgresql.org/docs/current/static/sql-createfunction.html
错误＃3：http://www.postgresql.org/docs/current/static/plpgsql-structure.html
错误＃6：http://www.postgresql.org/docs/current/static/plpgsql-declarations.html
错误＃7，＃8，＃9，＃10，＃12：http://www.postgresql.org/docs/current/static/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING
错误＃11：http://www.postgresql.org/docs/current/static/plpgsql-statements.html#PLPGSQL-STATEMENTS-ASSIGNMENT
错误＃14：http://www.postgresql.org/docs/current/static/plpgsql-control-structures.html#PLPGSQL-CONDITIONALS

不需要整个FOR循环且效率极低。它可以替换为：

SELECT sum(nofvotes)
  into sum_
FROM votes 
WHERE cid=scid AND bno=sbno;

Postgres有一个原生的布尔类型，使用它而不是整数更好。如果将函数声明为returns boolean，则最后一行可以简化为

return max_ > sum_;

这部分：

 select totvoters
   into max_
 from ballotbox 
 WHERE cid=scid AND bno=sbno;

如果cid，bno在表格选票箱中是唯一的，

仅才能正常工作。否则，如果select返回多行，则可能在运行时出现错误。

假设ballotbox上的select确实使用了主键（或唯一键），整个函数可以简化为一个小的SQL表达式：

create function trigf1(sbno integer, scid numeric(4,0))
  returns boolean
as
$body$
  return (select totvoters from ballotbox WHERE cid=scid AND bno=sbno) > 
         (SELECT sum(nofvotes) FROM votes WHERE cid=scid AND bno=sbno);
$body$
language sql;

Answer 2

我不是一个postgresSQL人，但我会想到

declare max as SELECT totvoters FROM ballotbox WHERE cid=scid AND bno=sbno;

应该是

declare max := SELECT totvoters FROM ballotbox WHERE cid=scid AND bno=sbno;

Answer 3

函数的主体应该是as 'code...'关键字后面的字符串，即CREATE FUNCTION trigf1(sbno integer, scid numeric(4,0)) RETURNS integer AS $$ BEGIN declare sum int default 0; declare max as SELECT totvoters FROM ballotbox WHERE cid=scid AND bno=sbno; for r as SELECT nofvotes FROM votes WHERE cid=scid AND bno=sbno; do set sum = sum + r.nofvotes; end for if sum > max then return(0); else return(1); END $$。通常使用A Closer Look at the Paint Mechanism：

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创建Postgres函数时出现语法错误

3 个答案: