概述
OceanBase是一款通用的分布式關系型數據庫，目前內部業務使用比較多有兩個版本：1.4和2.1。OceanBase每個版本變化總能帶給人很多驚喜，其中2.1版本實現了ORACLE很多特性的兼容。本文主要簡單瀏覽一下這些新功能。
運維
賬戶管理
在ORACLE Mode的租戶里，創建用戶依然是create user命令，密碼不用單引號。授權方式還是還是ORACLE和MySQL的結合。查看權限方式是MySQL的語法(這點還是MySQL語法很方便)。
在ORACLE Mode的租戶里，不同用戶就是不同SCHEMA,默認彼此數據訪問權限隔離，除非明確授權訪問。
$obclient -h11.***.84.84 -usys@tnt_oracle#obdemo -P2883 SYS -A -pobDBA2019
create user ora_user identified by 123456;
grant all privileges on ora_user.* to ora_user;
grant select on sys.* to ora_user;
show grants for ora_user;
select username, account_status, lock_date, expiry_date, created from dba_users;
實例變量查看
OceanBase集群級別的參數是通過查看和修改parameters，但是在Oracle租戶里，租戶級別的設置修改依然是通過類似修改MySQL的變量(variables)來的。這點跟Oracle原生實例不一樣。
show global variables where variable_name in ('autocommit','ob_compatibility_mode','ob_enable_sql_audit','ob_query_timeout','ob_read_consistency','ob_tcp_invited_nodes','ob_trx_timeout','sql_mode','tx_isolation','system_time_zone','time_zone');
修改方法舉例
set global autocommit=on;
性能分析
OceanBase實現了很多類似Oracle的AWR相關的GV$視圖。不過大部分在業務租戶下是沒有權限查看的。業務租戶下只提供了一個SQL全量日志視圖。這個也夠用了。詳細用法參見《阿里數據庫性能診斷的利器——SQL全量日志》
select /*+ read_consistency(weak) query_timeout(1000000000) */ request_time, svr_Ip, trace_id, sid, client_ip, tenant_id,tenant_name,user_name,db_name, query_sql, affected_rows,ret_code, event, state, elapsed_time, execute_time, queue_time, decode_time, get_plan_time, block_cache_hit, bloom_filter_cache_Hit, block_index_cache_hit, disk_reads,retry_cnt,table_scan, memstore_read_row_count, ssstore_read_row_count, round(request_memory_used/1024/1024) req_mem_mbfrom gv$sql_audit where user_name in ('ora_user') and rownum<100order by request_time desc ;
開發
面向開發的功能主要就是DDL和DML了。
DDL
建表
OceanBase的表是索引組織表(IOT)，強烈建議設置主鍵，並且主鍵就是數據。
建表時支持的數據類型如下：
-
CHAR/VARCHAR2 -
DATE/TIMESTAMP/TIMESTAMP WITH TIME ZONE/TIMESTAMP WITH LOCAL TIME ZONE -
INTERVAL(部分運算) -
NUMBER(包括其子類型int等) -
CLOB/BLOB(不超過48M)
建表示例：
$obclient -h11.***.84.84 -uora_user@tnt_oracle#obdemo -P2883 -A -p123456 ORA_USER
create table t01(
id number not null,
c1 char(10),
c2 varchar2(10),
c3 DATE default sysdate,
c4 timestamp default systimestamp,
c5 timestamp with time zone default localtimestamp,
c6 timestamp with local time zone default localtimestamp,
c7 int,
c8 clob,
c9 blob
);
create sequence seq_t01 start with 1000000000 increment by 2 cache 100 ;
insert into t01(id, c1, c2, c7, c8)
values(seq_t01.nextval, 'test', 'test',99999999999,'clobtextclobtextclobtextclobtextclobtextclobtextclobtextclobtextclobtext');
select * from t01\G
支持通過CTAS方法從老表創建新表。
修改表結構
目前對修改表結構類型還有很多限制，如只能在同類類型中改大值域。如varchar擴大長度。
函數
目前支持ORACLE常用的函數。如時間函數、數值函數、字符串函數、類型轉換函數、條件函數、系統函數、統計分析函數等等。
時間函數
目前支持：
-
interval -
localtimestamp -
current_timestamp -
sysdate/systimestamp
select sysdate, sysdate + interval'1' minute next_min, sysdate + interval'1' hour next_hour, sysdate + interval'1' day next_day from dual;
數值函數
目前支持：
-
abs/sign -
floor/'ceil` -
trunc/mod -
bitand
示例如下：
select abs(-3.1415926), ceil(3.1415926), floor(3.1415926), sign(-3.1415926),round(314 / 7, 0), mod(314,7), trunc(3.1415926) f
rom dual;
比較函數
目前支持：
-
least/greatest
字符串函數
目前支持：
-
pad/lpad/rpad -
instr/substr -
concat/|| -
length/lengthb -
lower/upper
select lpad(3.14159, 10, '*') c1, rpad('Apple', 10, '<') c2, ltrim(' Hello') c3, rtrim('World! ') c4, 'Hello ' || ' World' c5, concat('Hello ',' World!') c6, lower('Hello World!') c7, upper('Hello World!') c8, instr('Hello World','o',6) c9, substr('Hello World',5,3) c10, length('Hello 中國!') c11, lengthb('Hello 中國!') c12 from dual;
類型轉換函數
主要是數值、字符串、日期之間的互相轉換
目前支持：
-
to_date/to_timestamp -
to_char -
to_number
示例如下：
select cast('3.1415926' as number), to_date('2019-05-23 14:00:00','yyyy-mm-dd hh24:mi:ss'), to_number('3.1415926'), to_char(3.1415926), to_timestamp(sysdate), to_timestamp_tz(sysdate) from dual;
條件函數
目前支持：
-
case...when...end -
nvl -
decode
drop table t02;
create table t02(id number not null , type varchar2(2), gmt_create date not null default sysdate);
insert into t02(id,type) values(1,'R'),(2,'B'),(3,NULL);commit;
select id, NVL(type,'NULL!') type, case type when 'R' then 'Good guy!' when 'B' then 'Bad guy!' else 'Unknown!' end type_desc,
decode(type,'R','Good guy!','B','Bad guy!','Unknown!') type_desc2, gmt_create
from t02;
系統函數
目前支持：
-
uid/user
select uid, user, userenv('schemaid'),SYS_CONTEXT('userenv','current_user') from dual;
select rownum rn,object_name, object_type from user_objects order by object_name;
分析函數
目前支持的聚合函數包括：
-
COUNT -
APPROX_COUNT_DISTINCT -
SUM,MAX,MIN,AVG -
LISTAGG,RANK,DENSE_RANK,PERCENT_RANK+ROW_NUMBER -
NTILE,CUME_DIST,FIRST_VALUE,LAST_VALUE -
LEAD,LAG,NTH_VALUE
示例如下：
統計組內排名
select customernumber, checknumber, paymentdate, amount, dense_rank() over (partition by customernumber order by amount) dense_rank ,
round(PERCENT_RANK() over (partition by customernumber order by amount),2) perentage
from payments where customernumber=141 order by dense_rank, customernumber;
統計數量近似值
select count(distinct customernumber), APPROX_COUNT_DISTINCT(customernumber) from payments;
統計分組匯總
select * from (
select OFFICECODE, listagg(LASTNAME,',') within GROUP (ORDER BY EMPLOYEENUMBER) OVER (partition by OFFICECODE) EMP_LIST,
row_number() over (partition by OFFICECODE order by EMPLOYEENUMBER) as rn
FROM employees)
where rn = 1;
統計分組內第一和最后一個值
select OFFICECODE, listagg(LASTNAME,',') within GROUP (ORDER BY EMPLOYEENUMBER) OVER (partition by OFFICECODE) EMP_LIST,
first_value(LASTNAME) over (partition by OFFICECODE order by EMPLOYEENUMBER ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) first_emp_all,
last_value(LASTNAME) over (partition by OFFICECODE order by EMPLOYEENUMBER ) last_emp,
last_value(LASTNAME) over (partition by OFFICECODE order by EMPLOYEENUMBER ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) last_emp_all
FROM employees
order by OFFICECODE;
同行顯示分組統計的上一個和下一個值
select customernumber, checknumber, paymentdate,amount, round(cume_dist() over (partition by customernumber order by amount) ,2) as cume_dist ,lag(amount) over (partition by customernumber order by amount) last_ck,lead(amount) over (partition by customernumber order by amount) next_ckfrom payments where customernumber in (412,447,452,458) order by customernumber;
后記
更多Oracle的兼容性還在陸續開發或內部試用中。尤其是存儲過程、PLSQL以及Package。請保持關注。
OceanBase對Oracle的兼容只是用戶功能接口上的兼容，其底層原理依然是OceanBase特有的原理。
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