使用当前行和当前表名作为变量的触发函数（最后部分）

Question

就像我的第一个问题中详细介绍的那样，我有一个Postgres 9.1数据库，其中有多个表，这些表具有完全相同的列名，它们仅在列值上有所不同：

tbl_log_a
tbl_log_b
tbl_log_c
...

26 个表（从 a 到 z）。trfn_tbl_log_%letter%每个表都有一个触发器，它调用名为(from ato )的触发器函数z，该函数执行完全相同的操作：

CREATE OR REPLACE FUNCTION trfn_tbl_log_a_timetypespan()
  RETURNS trigger AS
$BODY$
DECLARE
v_timetype character varying;
v_timestmp_timetype timestamp without time zone;
v_timetypespan_resume interval;
v_stmtserial real;
v_sumtimetypespan_fnname interval;

BEGIN

IF NEW.timetype = 'lap' THEN
  SELECT timetype, timestmp, timetypespan FROM tbl_log_a WHERE fnname = NEW.fnname AND (timetype = 'start' OR timetype = 'resume') ORDER BY stmtserial DESC LIMIT 1 INTO v_timetype, v_timestmp_timetype, v_timetypespan_resume;
    IF v_timetype = 'start' THEN
      NEW.timetypespan := age(NEW.timestmp, v_timestmp_timetype);
    ELSIF v_timetype = 'resume' THEN
      SELECT timestmp FROM tbl_log_a WHERE fnname = NEW.fnname AND timetype = 'start' ORDER BY stmtserial DESC LIMIT 1 INTO v_timestmp_timetype;
      NEW.timetypespan := age(NEW.timestmp, v_timestmp_timetype) - v_timetypespan_resume;
    ELSE
      RAISE EXCEPTION USING MESSAGE = 'There is not any previous row...';
    END IF;

ELSIF NEW.timetype = 'resume' THEN
  SELECT timestmp FROM tbl_log_a WHERE fnname = NEW.fnname AND (timetype = 'start' OR timetype = 'lap') ORDER BY stmtserial DESC LIMIT 1 INTO v_timestmp_timetype;
    IF FOUND THEN
      NEW.timetypespan := age(NEW.timestmp, v_timestmp_timetype);
    ELSE
      RAISE EXCEPTION USING MESSAGE = 'There is not any previous row...';
    END IF;

ELSIF NEW.timetype = 'total' THEN
  SELECT stmtserial FROM tbl_log_a WHERE fnname = NEW.fnname AND timetype = 'total' ORDER BY stmtserial DESC LIMIT 1 INTO v_stmtserial;
  SELECT SUM(timetypespan) FROM (SELECT DISTINCT ON (floor(timeidx)::int) floor(timeidx)::int timeidx, timetypespan
  FROM tbl_log_a WHERE fnname = NEW.fnname AND timetype = 'lap' AND stmtserial > coalesce(v_stmtserial, 0) ORDER BY 1, 2 DESC) a INTO v_sumtimetypespan_fnname;
    IF v_sumtimetypespan_fnname NOTNULL THEN
      NEW.timetypespan := v_sumtimetypespan_fnname;
    ELSE
      RAISE EXCEPTION USING MESSAGE = 'There is not any previous row...';
    END IF;

END IF;
return NEW;

END
$BODY$
  LANGUAGE plpgsql VOLATILE;

触发器定义：

CREATE TRIGGER trfn_tbl_log_a_timetypespan
  BEFORE INSERT ON tbl_log_a
  FOR EACH ROW EXECUTE PROCEDURE trfn_tbl_log_a_timetypespan();

所以我必须创建 26 个触发器函数，每个tbl_log_%letter%. 我试图用一个通用的触发函数来替换它们。

我们在我之前的问题下通过简化的函数制定了动态 SQL 的解决方案。相同的技术可以扩展到这个更复杂的场景吗？

EXECUTE format($$...

Answer 1

是的，这应该有效（未经测试）：

CREATE OR REPLACE FUNCTION trfn_tbl_log_timetypespan()  -- generic name
  RETURNS trigger AS
$func$
DECLARE
   _timetype varchar;
   _timetypespan_resume interval;
   _ct int;
BEGIN

CASE NEW.timetype
WHEN 'lap' THEN
   EXECUTE format($$
      SELECT timetype, timetypespan, age($1, timestmp)
      FROM   %s
      WHERE  fnname = $2
      AND    timetype IN ('start', 'resume')
      ORDER  BY stmtserial DESC
      LIMIT  1$$
    , TG_RELID::regclass)
   USING NEW.timestmp, NEW.fnname
   INTO  _timetype, _timetypespan_resume, NEW.timetypespan;

   CASE _timetype
   WHEN 'start' THEN  -- do nothing

   WHEN 'resume' THEN
      EXECUTE format($$
         SELECT age($1, timestmp) - _timetypespan_resume
         FROM   %s
         WHERE  fnname = $2
         AND    timetype = 'start'
         ORDER  BY stmtserial DESC
         LIMIT  1$$
       , TG_RELID::regclass)
      USING NEW.timestmp, NEW.fnname
      INTO  NEW.timetypespan;

   ELSE
      RAISE EXCEPTION 'There is no previous row.';
   END CASE;

WHEN 'resume' THEN
   EXECUTE format($$
      SELECT age($1, timestmp)
      FROM   %s
      WHERE  fnname = $2
      AND    timetype IN ('start', 'lap')
      ORDER  BY stmtserial DESC LIMIT 1$$
    , TG_RELID::regclass)
   USING NEW.timestmp, NEW.fnname
   INTO  NEW.timetypespan;

   GET DIAGNOSTICS _ct = ROW_COUNT;

   IF _ct > 0 THEN  -- do nothing
   ELSE
      RAISE EXCEPTION 'There is no previous row.';
   END IF;

WHEN 'total' THEN
   EXECUTE format($$
      SELECT COALESCE(SUM(timetypespan), $1)
      FROM (
         SELECT floor(timeidx)::int, max(timetypespan) AS timetypespan
         FROM   %1$s
         WHERE  fnname = $2
         AND    timetype = 'lap'
         AND    stmtserial > coalesce(
                 (SELECT stmtserial
                  FROM   %1$s
                  WHERE  fnname = $2
                  AND    timetype = 'total'
                  ORDER  BY stmtserial DESC
                  LIMIT  1), 0)
         GROUP  BY 1
         ) sub$$
    , TG_RELID::regclass)
   USING NEW.timetypespan, NEW.fnname
   INTO  NEW.timetypespan;

   GET DIAGNOSTICS _ct = ROW_COUNT;

   IF _ct > 0 THEN  -- do nothing
   ELSE
      RAISE EXCEPTION 'There is no previous row.';
   END IF;
END CASE;

RETURN NEW;

END
$func$  LANGUAGE plpgsql;

这是我之前对您之前问题的回答的后续内容。在那里找到解释：

• 使用当前行和当前表名作为变量的触发函数

在做这件事的过程中，我简化了一些事情。SELECT就像：第一个分支中的第二个ELSIF只是SELECT上面一个级别的重复。我免费合并了它。

我还删除了一些不必要的中间步骤，并NEW直接分配给适用的字段。这就是为什么我可以删除你的大部分变量。

旁白：如果timeidx只有正数，您可以使用更便宜的trunc(timeidx)代替floor(timeidx)。

为了更容易地理解动态部分......

如果您只想为 - 即实现相同的功能，则（在应用and之后）tbl_log_a的有效执行代码如下所示：tbl_log_aformat()EXECUTE

...

CASE NEW.timetype
WHEN 'lap' THEN
   SELECT timetype, timetypespan, age(NEW.timestmp, timestmp)
   FROM   tbl_log_a
   WHERE  fnname = NEW.fnname
   AND    timetype IN ('start', 'resume')
   ORDER  BY stmtserial DESC
   LIMIT  1
   INTO  _timetype, _timetypespan_resume, NEW.timetypespan;

   CASE _timetype
   WHEN 'start' THEN  -- do nothing

   WHEN 'resume' THEN
      SELECT age(NEW.timestmp, timestmp) - _timetypespan_resume
      FROM   tbl_log_a
      WHERE  fnname = NEW.fnname
      AND    timetype = 'start'
      ORDER  BY stmtserial DESC
      LIMIT  1
      INTO  NEW.timetypespan;

...