最全的Oracle到高斯数据库的SQL语法迁移手册(建议收藏)

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筋斗云
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文章目录

概述

异构数据库的迁移(譬如从Oracle迁移到openGauss)工作主要包括三个方面,

  • 数据库对象的迁移,包括库、模式、表、索引、视图、触发器、存储过程等等;
  • 数据内容的迁移,主要指的是数据表中数据嘚迁移;
  • 数据应用的迁移,主要指的是应用中SQL语句的迁移。

目前对于数据库对象以及数据内容的迁移有很多成熟的工具,而对于应用迁移的工具却很少能够见到。原因是因为DML语句比DDL复杂的多,不同的数据库语法差异也比较大。目前市场上的迁移工具大多使用正则表达式来解析SQL语句,而DML语句的复杂性导致此类工具的解析成功率较低,难以作为一个成熟地商业产品进行推广。

PawSQL团队开发的DML语法转换工具Ora2ogSQL,通过PawSQL强大的SQLParser,能够解析几乎所有的Oracle语法,并将其转换为对应的openGauss语法,支持数据库应用的平滑迁移。

本手册介绍了Oracle和openGauss的语法区别,以及转换映射关系,可以作为迁移人员的SQL迁移参考手册。

本手册描述了PawSQL Ora2ogSQL内部的实现逻辑,PawSQL Ora2ogSQL能够帮助SQL迁移人员自动识别不兼容的语法,并完成语法转换。

虚拟表(dual)

虚拟表dual

Oracle获取一个常量需要通过一个dual,Opengauss不需要

编号OracleOpengauss
1select 2 from dualselect 2

虚拟列

虚拟列rownum

对于查询返回的每行数据,rownum虚拟列会返回一个数字,第一行的ROWNUM为1,第二行为2,以此类推。

  • rownum在select列表中时重写为row_number() over ()
  • rownum在where子句中时重写为limit… offset…
编号OracleOpengauss
1select rownum from customer;select row_number() over () as rownum from customer
2select tableoid from customer where rownum < 10 and rownum >= 2;select tableoid from customer limit 9 OFFSET 2
3select c_name from customer where rownum < 10 and c_phone = ‘111’;select customer.c_name from customer where customer.c_phone = ‘111’ limit 9
4select * from customer where rownum between 1 and 10;select tableoid from customer limit 10 OFFSET 0

虚拟列rowid

Oracle中的rowid虚拟列返回特定行的具体地址,在Opengauss中重写为tableoid || '#' || ctid

编号OracleOpengauss
1select rowid, c.* from customer c;select tableoid || ‘#’ || ctid, c.* from customer as c

字符串函数

nvl(col, value)

Oracle中的nvl(col, value)用来设置默认值,col为空就设置为value;

在Opengauss中重写为coalesce

编号OracleOpengauss
1select nvl(c_phone, 1) from customer;select coalesce(customer.c_phone, ‘1’) from customer

nvl2(col, v1, v2)

nvl2对col的null值进行处理,如果col为null,则返回v1, 否则返回v2;

postgre中没有类似的函数,可以重写为case… when…

编号OracleOpengauss
1select nvl2(c_phone, 1, 2) from customer;select case when c_phone is null then 1 else 2 end from customer

decode(arg1, arg2, arg3, arg4)

Oracle中的decode(arg1, arg2, arg3, arg4)函数, 表示当 arg1 等于 arg2 时,取 arg3,否则取 arg4。

postgre中没有类似的函数,可以重写为case… when…

编号OracleOpengauss
1select decode(c_phone,‘110’, 1 , 2) from customer;select case when c_phone = ‘110’ then 1 else 2 end from customer
2select decode(c_phone,null, 1 , 2) from customer;select case when c_phone is null then 1 else 2 end from customer

substr(str, int, int)

Oracle中的substr用来取一个字符串的子串,Opengauss有同名的函数实现类似功能。不同的是Oracle中,第二、第三个参数可以为负数,代表从后面进行计数,Opengauss不允许其为负数,需对其进行转换。Oracle中是以0开始计数,Opengauss以1开始计数(需确认)。

编号OracleOpengauss
1select substr(c_phone, 1 , -2 ) from customer;select substr(c_phone, 1, length(c_phone) - 2) from customer
2select substr(c_phone, -3 , 1 ) from customer;select substr(c_phone, length(c_phone) - 3, 1) from customer

instr(str1, str2)

Oracle中的instr用来取一个字符串的子串位置,当其只有两个参数时,表示子串的第一次出现的位置,和Opengauss中对应的函数为strpos。当其有多个参数时,无对应函数。

编号OracleOpengauss
1select instr(‘123’, ‘23’)select strpos(‘123’, ‘23’)

replace(srcstr, oldsub[, newsub ])

在Oracle中,replace()函数用于替换字符串, replace(srcstr, oldsub[, newsub ] ),和Opengauss中的replace函数用法基本一致。只是需要注意在Oracle中无第三个参数时,代表删除此字符,在Opengauss可将第三个参数设置为’'。

编号OracleOpengauss
1select replace(‘123’,‘1’);select replace(‘123’,‘1’,‘’);

stragg(str,[str])

Oracle里的stragg函数实现在分组内对列值的拼接,它和listagg类似,但是不可以指定拼接的顺序。在Opengauss中,可以使用string_agg函数来替换。其第二个参数可选,默认值为’',在Opengauss需补充第二个参数。

编号OracleOpengauss
1select listagg(c_name,‘,’) as name from customer group by c_phoneselect string_agg(c_name,‘,’) as name from customer group by c_phone
2select listagg(c_name) as name from customer group by c_phoneselect listagg(c_name,‘’) as name from customer group by c_phone

listagg(str, [str])

Oracle里的listagg函数实现对列值的拼接,它可以在分组内以指定顺序对非分组列进行拼接。在Opengauss中,可以使用string_agg函数来实现,需注意语法方面也有区别. 另外,其第二个参数可选,默认值为’',在Opengauss需补充第二个参数。

  • 当没有group by子句时,可以使用over(partiton by… order by…)进行替换

  • 当指定group by子句时,它的重写算法比较复杂

    • 如果需要保持拼接的顺序,需要通过子查询来实现(见编号2)
    • 如果不需要保持拼接顺序,可以把它转化为简单的聚集函数(编号3)
编号OracleOpengauss
1select listagg(c_name,‘,’) withingroup(orderby c_name) over (partitionby c_phone) as name from customer;sselect string_agg(customer.c_name, ‘,’) over (partition by customer.c_phone order by c_custkey) as name from customer
2select listagg(c_name,‘,’) within group(order by c_name) as name from customer group by c_phone;select max(paw_dt.name) as name from (select string_agg(customer.c_name, ‘,’) over (partition by customer.c_phone order by c_name) as name,
customer.c_phone
from customer) as paw_dt
group by c_phone
3select listagg(c_name,‘,’) within group(order by c_name) as name from customer group by c_phoneselect string_agg(c_name,‘,’) as name from customer group by c_phone

日期函数

sysdate/systimestamp

Oracle中的sysdate()/sysdate返回系统当前时间(日期+时分秒),在Opengauss中对应now()或是current_timestamp(日期+时分秒+毫秒)。

Oracle中的systimestamp返回系统当前时间戳(日期+时分秒+毫秒),在Opengauss中对应now()或是current_timestamp。

编号OracleOpengauss
1select sysdateselect current_timestamp
2select sysdate()select now()
3select systimestampselect current_timestamp

to_date(str, fmt)

Oracle中的to_date返回的是时间类型,而在Opengauss中to_date是日期类型,所以Oracle中的to_date在Opengauss中应该对应to_timestamp

编号OracleOpengauss
1select to_date( endTime ,‘yyyy-mm-dd hh24:mi:ss’) from tselect to_timestamp( endTime ,‘yyyy-mm-dd hh24:mi:ss’) from t

trunc(arg1, [arg2])

在Oracle中trunc函数有两种用法

  • 第一种是对数字进行截取, trunc(num,[int]); 是去掉数字num小数位以后的部分,并且不进行四舍五入。这种用法和在Opengauss的trunc用法一致,不需要转换

  • trunc函数的第二种用法是对日期进行提取,trunc(date,[fmt])。这种用法在Opengauss对应的函数是date_trunc(fmt, date),需注意在Opengauss中fmt是第一个参数,且不可省略。

编号OracleOpengauss
1select trunc( 111.23,2)select trunc( 111.23,2)
2select trunc(sysdate,‘year’)select date_trunc(‘year’, current_timestamp)
3select trunc(sysdate)select date_trunc(‘dd’, current_timestamp)

add_months(date, int)

Oracle中的add_months 函数主要是对日期函数进行操作,对日期按月增加。在Opengauss没有对应的函数,需将其转化为基于日期和interval的运算。

编号OracleOpengauss
1select add_months(sysdate, 2)select current_timestamp + 2 * interval ‘1 month’

last_day(date)

Oracle中的last_day返回指定日期所在月份的最后一天; 在Opengauss没有对应的函数,需将其转化为基于日期和interval的运算。

编号OracleOpengauss
1select add_months(sysdate, 2)select cast(date_trunc(‘MONTH’, current_timestamp) + interval ‘1 MONTH - 1 DAY’ as date)

SQL语句

HAVING子句顺序

Oracle允许HAVING在GROUP BY子句之前或之后。在Opengauss中,HAVING子句必须出现在GROUP BY子句后面。

编号OracleOpengauss
1select c_name from customer having count(*) > 2 group by c_nameselect c_name from customer group by c_name having count(*) > 2

括号中的表名

Oracle中单表引用允许使用括号括起来,Opengauss不允许。

编号OracleOpengauss
1SELECT * FROM (CUSTOMER);SELECT * FROM CUSTOMER;

UNIQUE关键字

Oracle中允许使用UNIQUE进行去重,在Opengauss中迁移为DISTINCT关键字

编号OracleOpengauss
1select unique c_phone from customerselect distinct customer.c_phone from customer

MINUS关键字

Oracle中可以使用minus关键字来取两个结果集的差,在Opengauss中需迁移为except.

编号OracleOpengauss
1select c_custkey from customer minus select o_custkey from ordersselect c_custkey from customer except select o_custkey from orders

FROM关键字

Oracle的delete语句的FROM关键字可以省略,迁移至Opengauss需补充上。

编号OracleOpengauss
1delete customer where 1=0;delete from customer where 1 = 0

NOLOGGING关键字

Oracle在执行INSERT语句时,可以通过指定NOLOGGING关键字来减少日志记录,提升操作性能。Opengauss不支持此关键字。

编号OracleOpengauss
1insert into customer nologging select * from customer_bk;insert into customer select * from customer_bk;

AS关键字

INSERT INTO 后面不需要添加as关键字,insert into ... as select... 修改为insert into... select...

编号OracleOpengauss
1insert into t as select c1 from t1insert into t select c1 from t1

FROM子查询的别名

Oracle中在不引起歧义的情况下子查询可以不带别名,而在Opengauss中,所有的FROM子查询都必须带有别名

编号OracleOpengauss
1select * from (select * from CUSTOMER)select * from (select * from CUSTOMER) as foo

UPDATE语句里的字段名

在Opengauss中,Update的时候,更新列不允许添加表名前缀。

编号OracleOpengauss
1update customer c set c.c_name = ‘xxx’ where c_custkey = 1;update customer set c_name = ‘xxx’ where c_custkey = 1

左(右)外连接

在Oracle中,外连接可以通过在条件上添加(+)来定义, 连接符(+)跟在哪个条件后面就是哪张表被左连。在Opengauss中,需将其重写为标准的外连接语法。

编号OracleOpengauss
1select * from customer, orders where c_custkey = o_custkey(+)select * from customer left outer join orders on c_custkey = o_custkey
2select * from customer, orders where c_custkey(+) = o_custkey and c_name(+) = o.o_clerk and o_custkey>100select * fromcustomer right outer join orders on (c_custkey = o_custkey and c_name = o_clerk) where o_custkey > 100

CONNECT BY子句

Oracle中,CONNECT BY 用于存在上下级等层级关系的数据表进行递归查询。语法格式: START WITH condition1 CONNECT BY [ NOCYCLE ] condition2。在Opengauss通过Recursive Common Table Expression来实现此功能,主要是把START WITH… CONNECT BY Prior拆成两个部分,查询表一致,但条件不一致,用UNION ALL合并.

编号OracleOpengauss
1select id from city_branch start with id=rolebranchid connect by prior id=parent_id;with RECURSIVE MIG_CTE as (
select id, 1 as level from city_branch where id = rolebranchid
union all
select id, level + 1 from city_branch, MIG_CTE where MIG_CTE.id = parent_id)
select * from MIG_CTE
2select t.branch_level, t.id from city_branch c where (c.branch_level = ‘1’ or t.branch_level = ‘2’) and (t.sign = ‘1’ or t.sign = ‘4’ or t.sign = ‘8’) and t.status = ‘1’ start with c.id = i_branch_id connect by c.id = prior c.parent_id order by c.branch_level descwith RECURSIVE MIG_CTE as
(select t.branch_level, t.id, 1 as level from city_branch as cwhere ((((branch_level = ‘1’ or t.branch_level = ‘2’)and ((t.sign = ‘1’ or t.sign = ‘4’) or t.sign = ‘8’)) and t.status = ‘1’) and c.id = i_branch_id)
union all
select t.branch_level, t.id, level + 1 from city_branch as c, MIG_CTE where ((((branch_level = ‘1’ or t.branch_level = ‘2’) and ((t.sign = ‘1’ or t.sign = ‘4’) or t.sign = ‘8’)) and t.status = ‘1’) and c.id = MIG_CTE.parent_id))
select * from MIG_CTE order by MIG_CTE.branch_level desc

操作符的强类型限制

Oracle中不同类型进行基于操作符的运算,会自动转化类型,譬如select 1 + '1' from dual。Opengauss是强类型,不同类型的运算会提示类型不匹配,执行select 1 + '1'会报错,需要进行显式的类型转换。

涉及的操作符类型包括:

操作符操作符名称
+加法
-减法
/除法
%取余
*乘法
||字符串拼接

数值运算(+,-,*,/,%)

编号OracleOpengauss
1select 1 + ‘1’select 1 + 1
2select 1 + charCol from tblselect 1 + cast(charCol as numeric) from tbl
3select ‘1’ - 1select 1- 1
4select 1 * charCol from tblselect 1 * **cast(charCol as numeric) ** from tbl
5select 1 / charCol from tblselect 1 /cast(charCol as numeric) from tbl
6select charCol % 2 from tblselect cast(charCol as numeric) % 2 from tbl

日期计算(+,-)

编号OracleOpengauss
1select sysdate - 1select current_timestamp - interval ‘1’ DAY
2select 1 + sysdate()select interval ‘1’ DAY + now()
3select systimestamp +1select current_timestamp + interval ‘1’ DAY
4select systimestamp - 1select current_timestamp - interval ‘1’ DAY

字符串拼接(||)

编号OracleOpengauss
1select 1||1select ‘1’||‘1’
2select 1 || c_custkeyselect 1 || cast(c_custkey as text)

函数参数的强类型限制

Oracle中在函数调用时,参数类型进行会自动转化类型,譬如 select substr(123.12,0,2)是合法的,且返回123。Opengauss是强类型, 执行select substr(123.12,0,2)会报错,需要进行显式的类型转换。

substr(arg1, arg2, arg3)

编号OracleOpengauss
1select substr(1234.1, 0, 4)select substr(‘1234.1’, 1, 4+1)
2select substr(‘1234.1’, 0, ‘2’)select substr(‘1234.1’, 0, 2)

sum(arg)

编号OracleOpengauss
1select sum(‘2’)select sum(2)

avg(arg)

编号OracleOpengauss
1select avg(‘2’)select avg(2)

round(arg)

编号OracleOpengauss
1select round(‘2’)select round(2)

条件判断中的强类型限制

Oracle中在进行条件判断时,左右表达式的类型进行会自动转化,譬如 where c_phone = 110是合法的。Opengauss是强类型, 执行where c_phone = 110会报错,需要进行显式的类型转换。

比较运算(=、>、<、>=、<=、<>)

转换原则,优先转换常量类型;当两个都为数据列时,优先转换左边的。

编号OracleOpengauss
1select * from customer where c_phone = 110select * from customer where c_phone = ‘110’
2select * from customer where ‘1’ = c_custkeyselect * from customer where 1 = c_custkey
3select * from customer where c_phone = c_custkeyselect * from customer where cast(c_phone as int) = c_custkey

BETWEEN

转换原则,转换 var0 between var1 and var2 中的 var1, var2。

编号OracleOpengauss
1select * from customer where c_custkey between ‘100’ and ‘200’;select * from customer where c_custkey between 100 and 200

IN LIST

转换原则,转换List中的变量。

编号OracleOpengauss
1select * from customer where c_phone in (110,120);select * from customer where c_phone in (‘110’, ‘120’)

默认参数

Oracle中有部分函数存在默认参数,而在Opengauss其参数是必填项。

to_char(unknown)

编号OracleOpengauss
1select to_char(c_custkey) from customerselect cast(c_custkey as text) from customer

to_number(str)

编号OracleOpengauss
1select to_number(‘100’)select 100
2select to_number(c_phone) from customer;select cast(c_phone as numeric) from customer

关于PawSQL

PawSQL专注数据库性能优化的自动化和智能化,支持MySQL,PostgreSQL,openGauss,Oracle等,提供的SQL优化产品包括

  • PawSQL Cloud,在线自动化SQL优化工具,支持SQL审查,智能查询重写、基于代价的索引推荐,适用于数据库管理员及数据应用开发人员,
  • PawSQL Advisor,IntelliJ 插件, 适用于数据应用开发人员,可以IDEA/DataGrip应用市场通过名称搜索“PawSQL Advisor”安装。
  • PawSQL Engine, 是PawSQL系列产品的后端优化引擎,可以独立安装部署,并通过http/json的接口提供SQL优化服务。PawSQL Engine以docker镜像的方式提供部署安装。
  • PawSQL Ora2pgSQL/PawsQL Ora2ogSQL,Oracle语法的SQL应用转换为PostgreSQL和openGauss语法的工具。

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