Update 20160827_01.md

Author: digoal

201608/20160827_01.md

@@ -39,18 +39,18 @@ INSERT 0 1000000
 update | delete limit 用法如下    
 
 ```  
-postgres=# with t1 as (select id from t where id between 1 and 1000 limit 10
+postgres=# with t1 as (select id from t where id between 1 and 1000 limit 10 for update
 )   
                   delete from t where id in (select * from t1);  
 DELETE 10  
   
-postgres=# with t1 as (select id from t where id between 1 and 1000 limit 10
+postgres=# with t1 as (select id from t where id between 1 and 1000 limit 10 for update
 )   
                    update t set info='new' where id in (select * from t1);  
 UPDATE 10  
   
 postgres=# explain with t1 as (select id from t where id between 1 and 1000 
-limit 10)   
+limit 10 for update)   
 postgres-#                    update t set info='new' where id in (select * 
 from t1);  
                                       QUERY 
@@ -76,15 +76,15 @@ width=4)
 
 ```  
 postgres=#  with t1 as (select ctid from t where id between 1 and 100000 
-limit 10) delete from t where ctid in (select ctid from t1) and id between 1 and 100000;   -- 一定要recheck防止ctid内容在此期间发生变化不符合查询条件, 或者使用RR模式 
+limit 10 for update) delete from t where ctid in (select ctid from t1) and id between 1 and 100000;   -- 一定要recheck防止ctid内容在此期间发生变化不符合查询条件, 或者使用RR模式 
 DELETE 10  
   
 postgres=#  with t1 as (select ctid from t where id between 1 and 100000 
-limit 10) update t set info='new' where ctid in (select ctid from t1) and id between 1 and 100000;  
+limit 10 for update) update t set info='new' where ctid in (select ctid from t1) and id between 1 and 100000;  
 UPDATE 10  
   
 postgres=# explain with t1 as (select ctid from t where id between 1 and 
-100000 limit 10) update t set info='new' where ctid in (select ctid from t1)  and id between 1 and 100000;  
+100000 limit 10 for update) update t set info='new' where ctid in (select ctid from t1)  and id between 1 and 100000;  
                                        QUERY 
 PLAN                                          
 -----------------------------------------------------------------------------
@@ -111,10 +111,10 @@ PLAN
 使用如下的写法即可：   
 
 ```
-postgres=# with t1 as (select ctid from test limit 10) delete from test where 
+postgres=# with t1 as (select ctid from test limit 10 for update) delete from test where 
 ctid = any (array(select ctid from t1)) and id between 1 and 100000;
 DELETE 10
-postgres=# with t1 as (select ctid from test limit 10) delete from test where 
+postgres=# with t1 as (select ctid from test limit 10 for update) delete from test where 
 ctid = any (array(select ctid from t1)) and id between 1 and 100000 returning *;
  id 
 ----
@@ -131,7 +131,7 @@ ctid = any (array(select ctid from t1)) and id between 1 and 100000 returning *;
 (10 rows)
 
 DELETE 10
-postgres=# with t1 as (select ctid from test limit 10) delete from test where 
+postgres=# with t1 as (select ctid from test limit 10 for update) delete from test where 
 ctid = any (array(select ctid from t1)) and id between 1 and 100000 returning *;
  id 
 ----
@@ -149,7 +149,7 @@ ctid = any (array(select ctid from t1)) and id between 1 and 100000 returning *;
 
 DELETE 10
   
-postgres=# explain with t1 as (select ctid from test limit 10) delete from 
+postgres=# explain with t1 as (select ctid from test limit 10 for update) delete from 
 test where ctid = any (array(select ctid from t1)) and id between 1 and 100000 returning *;
                                      QUERY 
 PLAN                                     
@@ -174,15 +174,15 @@ create table test(id int, crt_time timestamp);
 insert into test select generate_series(1,1000000), clock_timestamp();
 create index idx_test_1 on test(crt_time);
 
-postgres=# with t1 as (select ctid from test order by crt_time limit 1000) 
+postgres=# with t1 as (select ctid from test order by crt_time limit 1000 for update) 
 delete from test where ctid = any (array(select ctid from t1)) and id between 1 and 100000;
 DELETE 1000
 Time: 1.905 ms
-postgres=# with t1 as (select ctid from test order by crt_time limit 1000) 
+postgres=# with t1 as (select ctid from test order by crt_time limit 1000 for update) 
 delete from test where ctid = any (array(select ctid from t1)) and id between 1 and 100000;
 DELETE 1000
 Time: 1.470 ms
-postgres=# with t1 as (select ctid from test order by crt_time limit 1000) 
+postgres=# with t1 as (select ctid from test order by crt_time limit 1000 for update) 
 delete from test where ctid = any (array(select ctid from t1)) and id between 1 and 100000;
 DELETE 1000
 Time: 1.396 ms