plsql-在UPDATE-SET中使用平均最大值函数

我想更新另两列作为条件分组的列的值。假设表A A Char，b integer，c integer，d和A列可以包含相同的对象名，所以我想用以下条件更新表：如果列的A值和b值在两行row1:A1,2，numbery和row2:A1,2，numberx中找到，那么if:numberx，numbery>=0->AVGthird column，elsif numberx，numbery10

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创建表和示例数据：

SQL> create table t (a varchar2(20) not null
  2      , b number(38) not null
  3      , c number(38) not null
  4      , d varchar2(20) not null);

Table created.

SQL> insert into t values ('A1', 2, 10, 'b');

1 row created.

SQL> insert into t values ('A2', 7, -9, 'bc');

1 row created.

SQL> insert into t values ('A3', 7, 12, 'fg');

1 row created.

SQL> insert into t values ('A1', 2, 20, 'sa');

1 row created.

SQL> insert into t values ('A2', 7, 4, 'sa');

1 row created.

SQL> commit;

Commit complete.

为了帮助理解更新，创建一个查询，根据我的理解提供所需的结果：不是解决方案的一部分，只是解决方案的一部分

SQL> select t.a, t.b
  2      , case when agg_t.min_c >= 0 then avg_c -- all values of c are >= 0
  3          when agg_t.max_c < 0 then min_c -- all values of c are < 0
  4          else agg_t.max_c end as c
  5      , t.d
  6  from (select a, b, min(c) as min_c
  7          , max(c) as max_c , avg(c) as avg_c
  8     from t
  9     group by a, b) agg_t
 10  inner join t on agg_t.a = t.a and agg_t.b = t.b
 11  /

A                             B          C D
-------------------- ---------- ---------- --------------------
A3                            7         12 fg
A1                            2         15 sa
A2                            7          4 bc
A2                            7          4 sa
A1                            2         15 b

回滚到初始测试数据：

SQL> rollback;

Rollback complete.

此查询不会更新实际未进行更改的行，从而减少锁定、撤消和重做：

SQL> merge into T dest
  2  using (select a, b
  3          , case when min_c >= 0 then avg_c -- all values of c are >= 0
  4              when max_c < 0 then min_c -- all values of c are < 0
  5              else max_c end as new_c
  6      from (select a, b, min(c) as min_c
  7              , max(c) as max_c , avg(c) as avg_c
  8         from t
  9         group by a, b)) src
 10  on (dest.a = src.a and dest.b = src.b)
 11  when matched then update set c = new_c
 12  where c <> new_c
 13  or (c is null and new_c is not null)
 14  or (c is not null and new_c is null)
 15  /

3 rows merged.

SQL> 
SQL> select * from t;

A                             B          C D
-------------------- ---------- ---------- --------------------
A1                            2         15 b
A2                            7          4 bc
A3                            7         12 fg
A1                            2         15 sa
A2                            7          4 sa

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请尽量让它更具可读性。那是什么，某种奇怪的代数？

SQL> rollback;

Rollback complete.

SQL> merge into T dest
  2  using (select a, b
  3          , case when min_c >= 0 then avg_c -- all values of c are >= 0
  4              when max_c < 0 then min_c -- all values of c are < 0
  5              else max_c end as new_c
  6      from (select a, b, min(c) as min_c
  7              , max(c) as max_c , avg(c) as avg_c
  8         from t
  9         group by a, b)) src
 10  on (dest.a = src.a and dest.b = src.b)
 11  when matched then update set c = new_c
 12  where c <> new_c
 13  or (c is null and new_c is not null)
 14  or (c is not null and new_c is null)
 15  /

3 rows merged.

SQL> 
SQL> select * from t;

A                             B          C D
-------------------- ---------- ---------- --------------------
A1                            2         15 b
A2                            7          4 bc
A3                            7         12 fg
A1                            2         15 sa
A2                            7          4 sa