PostgreSQL 11 preview - MERGE 语法支持与CTE内支持，兼容SQL:2016 , 兼容 Oracle
背景
PostgreSQL 11 支持了merge 语法，兼容SQL 2016标准。并且支持用于CTE语法中。
merge 语法常用于合并数据（将 某个源表、values表达式、QUERY、临时表等 合并到某个目标表中）。
例如，将源表的变更日志，合并到物化视图中。
PostgreSQL 除了使用insert into on conflict，如今又多了merge语法的支持（可以更好的支持OLAP的数据批量合并场景）。
语法
https://www.postgresql.org/docs/devel/static/sql-merge.html
[ WITH with_query [, ...] ]
MERGE INTO target_table_name [ [ AS ] target_alias ]
USING data_source
ON join_condition
when_clause [...]
where data_source is
{ source_table_name |
( source_query )
}
[ [ AS ] source_alias ]
and when_clause is
{ WHEN MATCHED [ AND condition ] THEN { merge_update | merge_delete } |
WHEN NOT MATCHED [ AND condition ] THEN { merge_insert | DO NOTHING }
}
and merge_insert is
INSERT [( column_name [, ...] )]
[ OVERRIDING { SYSTEM | USER } VALUE ]
{ VALUES ( { expression | DEFAULT } [, ...] ) | DEFAULT VALUES }
and merge_update is
UPDATE SET { column_name = { expression | DEFAULT } |
( column_name [, ...] ) = ( { expression | DEFAULT } [, ...] )
} [, ...]
and merge_delete is
DELETE
返回
MERGE total-count
目标表触发器可能被触发
触发规则详见
https://www.postgresql.org/docs/devel/static/sql-merge.html
目标表规则不会被触发
如果JOIN过程中，匹配到多行，根据SQL标准定义来处理，目前是这样的，如果是更新的话，多行匹配（目标表的某单行，被源表或源数据的多行匹配到）会导致报错。
一些例子
1、Perform maintenance on CustomerAccounts based upon new Transactions.
MERGE INTO CustomerAccount CA -- 目标表
USING RecentTransactions T -- 源可以是表、query、(values (),(),....) as alias表达式 等
ON T.CustomerId = CA.CustomerId -- JOIN 条件
WHEN MATCHED THEN -- 记录匹配，可以引用使用源于目标中的字段
UPDATE SET Balance = Balance + TransactionValue
WHEN NOT MATCHED THEN -- 记录未匹配，只能引用源字段
INSERT (CustomerId, Balance)
VALUES (T.CustomerId, T.TransactionValue);
2、notice that this would be exactly equivalent to the following statement because the MATCHED result does not change during execution
MERGE INTO CustomerAccount CA
USING (Select CustomerId, TransactionValue From RecentTransactions) AS T
ON CA.CustomerId = T.CustomerId
WHEN NOT MATCHED THEN
INSERT (CustomerId, Balance)
VALUES (T.CustomerId, T.TransactionValue)
WHEN MATCHED THEN
UPDATE SET Balance = Balance + TransactionValue;
3、Attempt to insert a new stock item along with the quantity of stock. If the item already exists, instead update the stock count of the existing item. Don’t allow entries that have zero stock.
MERGE INTO wines w
USING wine_stock_changes s -- 源可以是临时表
ON s.winename = w.winename
WHEN NOT MATCHED AND s.stock_delta > 0 THEN
INSERT VALUES(s.winename, s.stock_delta)
WHEN MATCHED AND w.stock + s.stock_delta > 0 THEN
UPDATE SET stock = w.stock + s.stock_delta;
WHEN MATCHED THEN
DELETE;
The wine_stock_changes table might be, for example, a temporary table recently loaded into the database.
4、回归测试中的例子
+-- WITH referenced by MERGE statement
+CREATE TABLE m AS SELECT i AS k, (i || ' v')::text v FROM generate_series(1, 16, 3) i;
+ALTER TABLE m ADD UNIQUE (k);
+WITH RECURSIVE cte_basic AS (SELECT 1 a, 'cte_basic val' b)
+MERGE INTO m USING (select 0 k, 'merge source SubPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_basic WHERE cte_basic.a = m.k LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+ERROR: WITH RECURSIVE is not supported for MERGE statement
+-- Basic:
+WITH cte_basic AS (SELECT 1 a, 'cte_basic val' b)
+MERGE INTO m USING (select 0 k, 'merge source SubPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_basic WHERE cte_basic.a = m.k LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+-- Examine
+SELECT * FROM m where k = 0;
+ k | v
+---+----------------------
+ 0 | merge source SubPlan
+(1 row)
+
+-- See EXPLAIN output for same query:
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH cte_basic AS (SELECT 1 a, 'cte_basic val' b)
+MERGE INTO m USING (select 0 k, 'merge source SubPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_basic WHERE cte_basic.a = m.k LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+ QUERY PLAN
+-------------------------------------------------------------------
+ Merge on public.m
+ CTE cte_basic
+ -> Result
+ Output: 1, 'cte_basic val'::text
+ -> Hash Right Join
+ Output: o.k, o.v, o.*, m_1.ctid
+ Hash Cond: (m_1.k = o.k)
+ -> Seq Scan on public.m m_1
+ Output: m_1.ctid, m_1.k
+ -> Hash
+ Output: o.k, o.v, o.*
+ -> Subquery Scan on o
+ Output: o.k, o.v, o.*
+ -> Result
+ Output: 0, 'merge source SubPlan'::text
+ SubPlan 2
+ -> Limit
+ Output: ((cte_basic.b || ' merge update'::text))
+ -> CTE Scan on cte_basic
+ Output: (cte_basic.b || ' merge update'::text)
+ Filter: (cte_basic.a = m.k)
+(21 rows)
+
+-- InitPlan
+WITH cte_init AS (SELECT 1 a, 'cte_init val' b)
+MERGE INTO m USING (select 1 k, 'merge source InitPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_init WHERE a = 1 LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+-- Examine
+SELECT * FROM m where k = 1;
+ k | v
+---+---------------------------
+ 1 | cte_init val merge update
+(1 row)
+
+-- See EXPLAIN output for same query:
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH cte_init AS (SELECT 1 a, 'cte_init val' b)
+MERGE INTO m USING (select 1 k, 'merge source InitPlan' v) o ON m.k=o.k
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || ' merge update' FROM cte_init WHERE a = 1 LIMIT 1)
+WHEN NOT MATCHED THEN INSERT VALUES(o.k, o.v);
+ QUERY PLAN
+--------------------------------------------------------------------
+ Merge on public.m
+ CTE cte_init
+ -> Result
+ Output: 1, 'cte_init val'::text
+ InitPlan 2 (returns $1)
+ -> Limit
+ Output: ((cte_init.b || ' merge update'::text))
+ -> CTE Scan on cte_init
+ Output: (cte_init.b || ' merge update'::text)
+ Filter: (cte_init.a = 1)
+ -> Hash Right Join
+ Output: o.k, o.v, o.*, m_1.ctid
+ Hash Cond: (m_1.k = o.k)
+ -> Seq Scan on public.m m_1
+ Output: m_1.ctid, m_1.k
+ -> Hash
+ Output: o.k, o.v, o.*
+ -> Subquery Scan on o
+ Output: o.k, o.v, o.*
+ -> Result
+ Output: 1, 'merge source InitPlan'::text
+(21 rows)
+
+-- MERGE source comes from CTE:
+WITH merge_source_cte AS (SELECT 15 a, 'merge_source_cte val' b)
+MERGE INTO m USING (select * from merge_source_cte) o ON m.k=o.a
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || merge_source_cte.*::text || ' merge update' FROM merge_source_cte WHERE a = 15)
+WHEN NOT MATCHED THEN INSERT VALUES(o.a, o.b || (SELECT merge_source_cte.*::text || ' merge insert' FROM merge_source_cte));
+-- Examine
+SELECT * FROM m where k = 15;
+ k | v
+----+--------------------------------------------------------------
+ 15 | merge_source_cte val(15,"merge_source_cte val") merge insert
+(1 row)
+
+-- See EXPLAIN output for same query:
+EXPLAIN (VERBOSE, COSTS OFF)
+WITH merge_source_cte AS (SELECT 15 a, 'merge_source_cte val' b)
+MERGE INTO m USING (select * from merge_source_cte) o ON m.k=o.a
+WHEN MATCHED THEN UPDATE SET v = (SELECT b || merge_source_cte.*::text || ' merge update' FROM merge_source_cte WHERE a = 15)
+WHEN NOT MATCHED THEN INSERT VALUES(o.a, o.b || (SELECT merge_source_cte.*::text || ' merge insert' FROM merge_source_cte));
+ QUERY PLAN
+---------------------------------------------------------------------------------------------------------------
+ Merge on public.m
+ CTE merge_source_cte
+ -> Result
+ Output: 15, 'merge_source_cte val'::text
+ InitPlan 2 (returns $1)
+ -> CTE Scan on merge_source_cte merge_source_cte_1
+ Output: ((merge_source_cte_1.b || (merge_source_cte_1.*)::text) || ' merge update'::text)
+ Filter: (merge_source_cte_1.a = 15)
+ InitPlan 3 (returns $2)
+ -> CTE Scan on merge_source_cte merge_source_cte_2
+ Output: ((merge_source_cte_2.*)::text || ' merge insert'::text)
+ -> Hash Right Join
+ Output: merge_source_cte.a, merge_source_cte.b, ROW(merge_source_cte.a, merge_source_cte.b), m_1.ctid
+ Hash Cond: (m_1.k = merge_source_cte.a)
+ -> Seq Scan on public.m m_1
+ Output: m_1.ctid, m_1.k
+ -> Hash
+ Output: merge_source_cte.a, merge_source_cte.b
+ -> CTE Scan on merge_source_cte
+ Output: merge_source_cte.a, merge_source_cte.b
+(20 rows)
+
+DROP TABLE m;
5、个人测试例子
目标表触发器
create or replace function tg() returns trigger as $$
declare
begin
raise notice '%', new;
return null;
end;
$$ language plpgsql strict;
目标表
create table t1(id int primary key, info text, crt_time timestamp);
源表
create table t2(id int primary key, info text, crt_time timestamp);
写入100条测试数据到源表
postgres=# insert into t2 select generate_series(1,100),random()*100, now();
INSERT 0 100
创建目标表触发器
postgres=# create trigger tg after insert on t1 for each row execute procedure tg();
CREATE TRIGGER
使用merge into，将源表数据合并到目标表，并触发了INSERT触发器
postgres=#
merge into t1 using t2
on t1.id=t2.id
when not matched then insert (id,info,crt_time) values (t2.id,t2.info,t2.crt_time)
when matched and t1.info<>t2.info or t1.crt_time<>t2.crt_time then update set info=t2.info , crt_time=t2.crt_time;
NOTICE: (1,29.9749359954149,"2018-04-07 22:03:31.531152")
NOTICE: (2,93.1852474343032,"2018-04-07 22:03:31.531152")
NOTICE: (3,25.758066913113,"2018-04-07 22:03:31.531152")
NOTICE: (4,69.128438225016,"2018-04-07 22:03:31.531152")
NOTICE: (5,34.7714505158365,"2018-04-07 22:03:31.531152")
NOTICE: (6,47.4942798726261,"2018-04-07 22:03:31.531152")
NOTICE: (7,61.8766254279763,"2018-04-07 22:03:31.531152")
NOTICE: (8,97.1885625738651,"2018-04-07 22:03:31.531152")
NOTICE: (9,7.41707538254559,"2018-04-07 22:03:31.531152")
NOTICE: (10,70.8636813331395,"2018-04-07 22:03:31.531152")
NOTICE: (11,33.8312264997512,"2018-04-07 22:03:31.531152")
NOTICE: (12,77.4763741064817,"2018-04-07 22:03:31.531152")
NOTICE: (13,5.14419632963836,"2018-04-07 22:03:31.531152")
NOTICE: (14,86.3092178478837,"2018-04-07 22:03:31.531152")
NOTICE: (15,41.1678662057966,"2018-04-07 22:03:31.531152")
NOTICE: (16,27.8295359108597,"2018-04-07 22:03:31.531152")
NOTICE: (17,77.8380565810949,"2018-04-07 22:03:31.531152")
NOTICE: (18,13.997572241351,"2018-04-07 22:03:31.531152")
NOTICE: (19,34.8465123679489,"2018-04-07 22:03:31.531152")
NOTICE: (20,26.4941859059036,"2018-04-07 22:03:31.531152")
NOTICE: (21,88.9189361128956,"2018-04-07 22:03:31.531152")
NOTICE: (22,21.6747588012367,"2018-04-07 22:03:31.531152")
NOTICE: (23,41.413659369573,"2018-04-07 22:03:31.531152")
NOTICE: (24,19.375761738047,"2018-04-07 22:03:31.531152")
NOTICE: (25,53.5534802824259,"2018-04-07 22:03:31.531152")
NOTICE: (26,82.7209649607539,"2018-04-07 22:03:31.531152")
NOTICE: (27,39.306652918458,"2018-04-07 22:03:31.531152")
NOTICE: (28,41.2743093911558,"2018-04-07 22:03:31.531152")
NOTICE: (29,79.2670299764723,"2018-04-07 22:03:31.531152")
NOTICE: (30,40.3565632645041,"2018-04-07 22:03:31.531152")
NOTICE: (31,54.4456570409238,"2018-04-07 22:03:31.531152")
NOTICE: (32,9.24196597188711,"2018-04-07 22:03:31.531152")
NOTICE: (33,33.5418107453734,"2018-04-07 22:03:31.531152")
NOTICE: (34,80.203724000603,"2018-04-07 22:03:31.531152")
NOTICE: (35,78.3704041969031,"2018-04-07 22:03:31.531152")
NOTICE: (36,68.3132612612098,"2018-04-07 22:03:31.531152")
NOTICE: (37,27.698003873229,"2018-04-07 22:03:31.531152")
NOTICE: (38,40.2470296714455,"2018-04-07 22:03:31.531152")
NOTICE: (39,65.5018238350749,"2018-04-07 22:03:31.531152")
NOTICE: (40,35.1150792557746,"2018-04-07 22:03:31.531152")
NOTICE: (41,11.110711004585,"2018-04-07 22:03:31.531152")
NOTICE: (42,99.3330503813922,"2018-04-07 22:03:31.531152")
NOTICE: (43,12.5914534088224,"2018-04-07 22:03:31.531152")
NOTICE: (44,16.2549073807895,"2018-04-07 22:03:31.531152")
NOTICE: (45,85.6422682292759,"2018-04-07 22:03:31.531152")
NOTICE: (46,53.759319614619,"2018-04-07 22:03:31.531152")
NOTICE: (47,44.0844432916492,"2018-04-07 22:03:31.531152")
NOTICE: (48,63.4803248103708,"2018-04-07 22:03:31.531152")
NOTICE: (49,67.75689185597,"2018-04-07 22:03:31.531152")
NOTICE: (50,78.9309556595981,"2018-04-07 22:03:31.531152")
NOTICE: (51,89.9745107628405,"2018-04-07 22:03:31.531152")
NOTICE: (52,56.6758279688656,"2018-04-07 22:03:31.531152")
NOTICE: (53,0.60571450740099,"2018-04-07 22:03:31.531152")
NOTICE: (54,31.3881701324135,"2018-04-07 22:03:31.531152")
NOTICE: (55,76.0515897534788,"2018-04-07 22:03:31.531152")
NOTICE: (56,54.1591947898269,"2018-04-07 22:03:31.531152")
NOTICE: (57,14.1091350931674,"2018-04-07 22:03:31.531152")
NOTICE: (58,15.3582426719368,"2018-04-07 22:03:31.531152")
NOTICE: (59,95.4335042275488,"2018-04-07 22:03:31.531152")
NOTICE: (60,93.3761650696397,"2018-04-07 22:03:31.531152")
NOTICE: (61,55.714805983007,"2018-04-07 22:03:31.531152")
NOTICE: (62,49.8791612684727,"2018-04-07 22:03:31.531152")
NOTICE: (63,2.61813104152679,"2018-04-07 22:03:31.531152")
NOTICE: (64,89.2566167283803,"2018-04-07 22:03:31.531152")
NOTICE: (65,30.0828852690756,"2018-04-07 22:03:31.531152")
NOTICE: (66,80.988535284996,"2018-04-07 22:03:31.531152")
NOTICE: (67,57.5698779895902,"2018-04-07 22:03:31.531152")
NOTICE: (68,57.7808891423047,"2018-04-07 22:03:31.531152")
NOTICE: (69,21.2355649564415,"2018-04-07 22:03:31.531152")
NOTICE: (70,23.0717018712312,"2018-04-07 22:03:31.531152")
NOTICE: (71,92.8959684446454,"2018-04-07 22:03:31.531152")
NOTICE: (72,32.3462759610265,"2018-04-07 22:03:31.531152")
NOTICE: (73,22.4047522526234,"2018-04-07 22:03:31.531152")
NOTICE: (74,5.48742185346782,"2018-04-07 22:03:31.531152")
NOTICE: (75,48.6011833418161,"2018-04-07 22:03:31.531152")
NOTICE: (76,8.04702048189938,"2018-04-07 22:03:31.531152")
NOTICE: (77,59.2467414680868,"2018-04-07 22:03:31.531152")
NOTICE: (78,92.6856266334653,"2018-04-07 22:03:31.531152")
NOTICE: (79,71.5273452922702,"2018-04-07 22:03:31.531152")
NOTICE: (80,27.003633370623,"2018-04-07 22:03:31.531152")
NOTICE: (81,71.6165823396295,"2018-04-07 22:03:31.531152")
NOTICE: (82,61.5018560551107,"2018-04-07 22:03:31.531152")
NOTICE: (83,83.6794613394886,"2018-04-07 22:03:31.531152")
NOTICE: (84,72.2222968470305,"2018-04-07 22:03:31.531152")
NOTICE: (85,92.8900261875242,"2018-04-07 22:03:31.531152")
NOTICE: (86,59.7310510929674,"2018-04-07 22:03:31.531152")
NOTICE: (87,26.3814916368574,"2018-04-07 22:03:31.531152")
NOTICE: (88,6.99916132725775,"2018-04-07 22:03:31.531152")
NOTICE: (89,75.0892938114703,"2018-04-07 22:03:31.531152")
NOTICE: (90,21.8149958644062,"2018-04-07 22:03:31.531152")
NOTICE: (91,0.375326396897435,"2018-04-07 22:03:31.531152")
NOTICE: (92,30.8040997944772,"2018-04-07 22:03:31.531152")
NOTICE: (93,71.694157179445,"2018-04-07 22:03:31.531152")
NOTICE: (94,2.99345748499036,"2018-04-07 22:03:31.531152")
NOTICE: (95,20.0607165228575,"2018-04-07 22:03:31.531152")
NOTICE: (96,1.77704244852066,"2018-04-07 22:03:31.531152")
NOTICE: (97,83.9819927699864,"2018-04-07 22:03:31.531152")
NOTICE: (98,77.6305945124477,"2018-04-07 22:03:31.531152")
NOTICE: (99,59.5579316373914,"2018-04-07 22:03:31.531152")
NOTICE: (100,5.21755772642791,"2018-04-07 22:03:31.531152")
MERGE 100
再次执行，由于设置了条件t1.info<>t2.info or t1.crt_time<>t2.crt_time才更新，所以MERGE 0条.
postgres=# merge into t1 using t2
on t1.id=t2.id
when not matched then insert (id,info,crt_time) values (t2.id,t2.info,t2.crt_time)
when matched and t1.info<>t2.info or t1.crt_time<>t2.crt_time then update set info=t2.info , crt_time=t2.crt_time;
MERGE 0
把条件t1.info<>t2.info or t1.crt_time<>t2.crt_time去掉，MERGE了100条(update)
postgres=#
merge into t1 using t2
on t1.id=t2.id
when not matched then insert (id,info,crt_time) values (t2.id,t2.info,t2.crt_time)
when matched then update set info=t2.info , crt_time=t2.crt_time;
MERGE 100
目前merge into语法与rule不能同时使用，也就是说如果目标表上有insert\update\delete的RULE的话，不能使用merge into来合并数据到目标表。
postgres=# create rule r1 as on insert to t1 do instead nothing;
CREATE RULE
postgres=# insert into t1 values (0);
INSERT 0 0
postgres=# truncate t1;
TRUNCATE TABLE
postgres=# \set VERBOSITY verbose
postgres=# merge into t1 using t2
on t1.id=t2.id
when not matched then insert (id,info,crt_time) values (t2.id,t2.info,t2.crt_time)
when matched and t1.info<>t2.info or t1.crt_time<>t2.crt_time then update set info=t2.info , crt_time=t2.crt_time;
ERROR: 0A000: MERGE is not supported for relations with rules
LOCATION: transformMergeStmt, parse_merge.c:424
参考
https://www.postgresql.org/docs/devel/static/sql-merge.html
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=e6597dc3533946b98acba7871bd4ca1f7a3d4c1d
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=354f13855e6381d288dfaa52bcd4f2cb0fd4a5eb
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=7cf8a5c302735d193dcf901b87e03e324903c632
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=aa5877bb26347c58a34aee4e460eb1e1123bb096
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=d204ef63776b8a00ca220adec23979091564e465
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=83454e3c2b28141c0db01c7d2027e01040df5249
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=aa3faa3c7a7a49b3318059ccaf79bc1886a64707
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=4923550c20ae6d122ae0867480a7de8b040f7d80