KingbaseES 实现 MYSQL 的 delete limit 写法

使用MySQL的用户可能会比较熟悉这样的用法，更新或删除时可以指定限制更新或删除多少条记录。

update tl set xxx=xxx where xxx limit 10;

delete from tl where xxx limit 10;

目前KingbaseES没有类似的语法，但是可以通过子查询来达到同样的效果。

创建测试表

test=# create table t1(id number, uid number);
CREATE TABLE
test=# insert into t1 SELECT generate_series(1,20000),(random()*(10^7))::integer;
INSERT 0 20000

update | delete limit 子查询写法

test=# DELETE FROM t1 WHERE id in(SELECT id FROM t1 ORDER BY id limit 10);
DELETE 10

test=# update t1 set uid=999 where id in (select id from t1 where id between 50 and 200 limit 30);
UPDATE 30
test=# select * from t1 where id between 50 and 200;
 id  |   uid   
-----+---------
  61 |     999
  62 |     999
  63 |     999
  64 |     999
  65 |     999
  66 |     999
  67 |     999
  68 |     999
  69 |     999
  70 |     999
  71 |     999
  72 |     999
  73 |     999
  74 |     999
  75 |     999
  76 |     999
  77 |     999
  78 |     999
  79 |     999
  80 |     999
  81 |     999
  82 |     999
  83 |     999
  84 |     999
  85 |     999
  86 |     999
  87 |     999
  88 |     999
  89 |     999
  90 |     999
  91 | 4791280
  92 | 8658152
  93 | 4275799
  94 | 1188468
  95 | 4405454
  96 | 6355264
  97 | 3400361
  98 | 7912872
  99 | 4159834
 100 | 8621857