openGuass每日一练第16天|事务控制 from seven
学习目标
学习openGauss事务控制
事务是用户定义的一个数据库操作序列，这些操作要么全做要么全不做，是一个不可分割的工作单位
课程学习
连接数据库
#第一次进入等待15秒#数据库启动中...
su - omm
gsql -r
1.事务控制
–通过START TRANSACTION和BEGIN语法启动事务
-以默认方式启动事务
select * from pg_class limit 1;
END;
–开启一个事务，设置事务的隔离级别为READ
BEGIN;
SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
show transaction_read_only;
select * from pg_class limit 1;
create schema tpcds10;
commit;
–以隔离级别为repeatable read，读/写方式启动事务
START TRANSACTION ISOLATION LEVEL repeatable read READ WRITE;
show transaction_isolation;
show transaction_read_only;
select * from pg_class limit 1;
create schema tpcds10;
rollback;
–事务回滚，schema没有创建成功
\dn+ tpcds10;
2.savepoint
–保存点是事务中的一个特殊记号，它允许将那些在它建立后执行的命令全部回滚，把事务的状态恢复到保存点所在的时刻
START TRANSACTION;
INSERT INTO table1 VALUES (1);
–建立保存点
INSERT INTO table1 VALUES (2);
–回滚保存点
ROLLBACK TO SAVEPOINT my_savepoint;
–删除保存点
INSERT INTO table1 VALUES (3);
COMMIT;
–查询表的内容，会同时看到1和3,不能看到2，因为2被回滚
课程作业
1. 以默认方式启动事务1，修改事务隔离级别，查看transaction_isolation
omm=# start transaction;
START TRANSACTION
omm=# show transaction_isolation;
transaction_isolation
-----------------------
read committed
(1 row)
omm=# set transaction isolation level repeatable read;
SET
omm=# show transaction_isolation;
transaction_isolation
-----------------------
repeatable read
(1 row)
omm=# create table t1(id int);
CREATE TABLE
omm=# insert into t1 values(1);
INSERT 0 1
omm=# select * from t1;
id
----
1
(1 row)
omm=# insert into t1 values(2);
omm=# INSERT 0 1
select * from t1;
omm=# id
----
1
2
(2 rows)
omm=# commit;
omm=# COMMIT
2. 以读写方式启动事务2，创建新表，修改事务为只读事务，查看transaction_read_only，并向表中插入记录
omm=# start transaction isolation level repeatable read read write;
START TRANSACTION
omm=# show transaction_isolation;
transaction_isolation
-----------------------
repeatable read
(1 row)
omm=# show transaction_read_only;
transaction_read_only
-----------------------
off
(1 row)
omm=# insert into t1 values(4);
INSERT 0 1
omm=# commit;
COMMIT
omm=# select * from t1;
id
----
1
2
4
(3 rows)
3. 启动事务3，对表进行增删改查，并用到创建savepoint，回滚savepoint和删除savepoint
omm=# start transaction;
START TRANSACTION
omm=# show transaction_isolation;
transaction_isolation
-----------------------
read committed
(1 row)
omm=# show transaction_read_only;
transaction_read_only
-----------------------
off
(1 row)
omm=# create table t2(id int);
CREATE TABLE
omm=# insert into t2 values(1);
INSERT 0 1
omm=# savepoint my_sp1;
SAVEPOINT
omm=# insert into t2 values(2);
INSERT 0 1
omm=# rollback to savepoint my_sp1;
ROLLBACK
omm=# insert into t2 values(3);
INSERT 0 1
omm=# commit;
COMMIT
omm=# select * from t2;
id
----
1
3
(2 rows)
4. 清理数据
omm=# \d
omm=# List of relations
Schema | Name | Type | Owner | Storage
--------+--------+-------+-------+----------------------------------
public | t1 | table | omm | {orientation=row,compression=no}
public | t2 | table | omm | {orientation=row,compression=no}
public | table1 | table | omm | {orientation=row,compression=no}
(3 rows)
omm=# drop table t1;
DROP TABLE
omm=# drop table t2;
DROP TABLE
omm=# drop table table1;
DROP TABLE
