[英]SQL CTE Syntax to DELETE / INSERT rows
从表中删除 ,然后插入到同一表并返回insert的值的CTE语法是什么?
进行2个小时的睡眠操作,看起来有些不适(除了无法执行操作外):
WITH delete_rows AS (
DELETE FROM <some_table> WHERE id = <id_value>
RETURNING *
)
SELECT * FROM delete_rows
UNION
(
INSERT INTO <some_table> ( id, text_field )
VALUES ( <id_value>, '<text_field_value>' )
RETURNING *
)
预期的行为是首先清除ID的所有记录,然后插入相同ID的记录(故意不是upsert),然后返回那些插入的记录(而不是删除记录)。
您的问题更新清楚地表明,您无法在单个语句中执行此操作。
打包到同一条语句的CTE中,这两个操作( INSERT
和DELETE
)将看到表的相同快照,并且实际上在同一时间执行。 即, INSERT
仍会看到您认为已删除的所有行。 每个文档:
所有语句都使用相同的快照执行(请参见第13章),因此它们无法“看到”彼此对目标表的影响。
您可以将它们作为两个独立的语句包装到同一个事务中-似乎也不是必须的,但是它将使整个操作自动完成/失败:
BEGIN;
DELETE FROM <some_table> WHERE id = <id_value>;
INSERT INTO <some_table> (id, text_field)
VALUES ( <id_value>, '<text_field_value>')
RETURNING *;
COMMIT;
现在, INSERT
可以看到DELETE
的结果。
CREATE TABLE test_table (value TEXT UNIQUE);
INSERT INTO test_table SELECT 'value 1';
INSERT INTO test_table SELECT 'value 2';
WITH delete_row AS (DELETE FROM test_table WHERE value='value 2' RETURNING 0)
INSERT INTO test_table
SELECT DISTINCT 'value 2'
FROM (SELECT 'dummy') dummy
LEFT OUTER JOIN delete_row ON TRUE
RETURNING *;
上面的查询处理DELETE删除0/1 /一些行时的情况。
详细介绍一下skif1979的“ DelSert” CTE方法“ Logged DelSert:”
-- setups
DROP TABLE IF EXISTS _zx_t1 ;
CREATE TEMP TABLE
IF NOT EXISTS
_zx_t1
( id bigint
, fld2 bigint
, UNIQUE (id)
);
-- unique records
INSERT INTO _zx_t1 SELECT 1, 99;
INSERT INTO _zx_t1 SELECT 2, 98;
WITH
_cte_del_row AS
( DELETE
FROM _zx_t1
WHERE id = 2
RETURNING id as _b4_id, fld2 as _b4_fld2 -- returns complete deleted row
)
, _cte_delsert AS
( INSERT
INTO _zx_t1
SELECT DISTINCT
_cte_del_row._b4_id
, _cte_del_row._b4_fld2 + 1
from (SELECT null::integer AS _zunk) _zunk -- skif1979's trick here
LEFT OUTER JOIN _cte_del_row -- clever LOJ magic
ON TRUE -- LOJ cartesian product
RETURNING id as _aft_id , fld2 as _aft_fld2 -- return newly "delserted" rows
)
SELECT * -- returns before & after snapshots from CTE's
FROM
_cte_del_row
, _cte_delsert ;
RESULT:
_b4_id | _b4_fld2 | _aft_id | _aft_fld2
--------+----------+---------+-----------
2 | 209 | 2 | 210
AFAICT这些全部以工作单元的形式线性发生,类似于日记或记录的更新。
适用于
不适用于
与“ Logged DelSert”类似的一个相关(更好的是IMO)答案是,已记录的“ SelUp”:
-- setups
DROP TABLE IF EXISTS _zx_t1 ;
CREATE TEMP TABLE
IF NOT EXISTS
_zx_t1
( id bigint
, fld2 bigint
, UNIQUE (id)
);
-- unique records
INSERT INTO _zx_t1 SELECT 1, 99;
INSERT INTO _zx_t1 SELECT 2, 98;
WITH
_cte_sel_row AS
( SELECT -- start unit of work with read
id as _b4_id -- fields need to be aliased
,fld2 as _b4_fld2 -- to prevent ambiguous column errors
FROM _zx_t1
WHERE id = 2
FOR UPDATE
)
, _cte_sel_up_ret AS -- we're in the same UOW
( UPDATE _zx_t1 -- actual table
SET fld2 = _b4_fld2 + 1 -- some actual work
FROM _cte_sel_row
WHERE id = _b4_id
AND fld2 < _b4_fld2 + 1 -- gratuitous but illustrates the point
RETURNING id as _aft_id, fld2 as _aft_fld2
)
SELECT
_cte_sel_row._b4_id
,_cte_sel_row._b4_fld2 -- before
,_cte_sel_up_ret._aft_id
,_cte_sel_up_ret._aft_fld2 -- after
FROM _cte_sel_up_ret
INNER JOIN _cte_sel_row
ON TRUE AND _cte_sel_row._b4_id = _cte_sel_up_ret._aft_id
;
RESULT:
_b4_id | _b4_fld2 | _aft_id | _aft_fld2
--------+----------+---------+-----------
2 | 209 | 2 | 210
另请参阅: https : //rob.conery.io/2018/08/13/transactional-data-operations-in-postgresql-using-common-table-expressions/
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