GaussDB: db2->gaussdb 函数转换

一、db2->gaussdb函数转换

问题描述：使用GaussDB替代DB2的方案，使用起来还是有些差别，做一下函数的映射转换。

	DB2写法	GaussDB改写语法
日期函数	days(OUTWORKDATE)	EXTRACT(epoch from outworkdate) /86400; EXTRACT(DAY FROM (OUTWORKDATE - DATE '0001-01-01' + INTEGER '1' ))
	day(OUTWORKDATE)	EXTRACT(DAY FROM outworkdate); DATE_PART('DAY', OUTWORKDATE)
	month(current_date)	EXTRACT(MONTH FROM current_date); DATE_PART('MONTH', TRUNC(CURRENT_DATE))
	year(current_date)	EXTRACT(YEAR FROM outworkdate); DATE_PART('YEAR', TRUNC(CURRENT_DATE))
	CURRENT_DATE -1 DAY/MONTH/YEAR	CURRENT_DATE - INTERVAL '1 day' AS yesterday, CURRENT_DATE - INTERVAL '1 month' AS last_month, CURRENT_DATE - INTERVAL '1 year' AS last_year; TRUNC(CURRENT_DATE) - INTERVAL '1 DAY' AS yesterday, TRUNC(CURRENT_DATE) - INTERVAL '1 MONTH' AS last_month, TRUNC(CURRENT_DATE) - INTERVAL '1 YEAR' AS last_year;
	CURRENT_DATE -1 DAY -1 MONTH	current_date - interval '1 DAY' - interval '1 MONTH'
	to_char(CURRENT_DATE,'yyyy-mm')	to_char(current_date,'yyyy-mm');to_char(trunc(current_date),'yyyy-mm')
	TIMESTAMPDIFF(2,END_TIME - START_TIME)	extract(epoch from (end_time - start_time)); trunc(extract(epoch from (end_time - start_time))); TIMESTAMPDIFF()函数只在mysql模式中可以使用
数据类型转化	dec(RATE,10,2)	rate::numeric(10,2); cast(rate as numeric(10,2));
	int(100.123)	cast(100.123 as int); 100.123::int;
	char(1)	cast(1 as char(1))
	to_date()	to_date()
	to_char()	to_char()
其他常用函数	LOCATE('|','115|56',1)	INSTR('115|56', '|', 1)
	listagg(name,',')	listagg(b,';') within group (order by b)
	nvl()	nvl()
	trim()	trim(BOTH 'x' from 'xTommxx'); trim(leading 'x' from 'xTommxx'); trim(trailing 'x' from 'xTommxx');
	substr()	substr('stringtest' from 4); substr('stringtest',4);
	VALUE()	COALESCE()
	floor()	floor()
	round()	round()
	coalesce(company,0)	coalesce(company,0)
	length()	length()
	POSSTR(EXP1,EXP2)	position(exp1,exp2)
	REPLACE (EXP1,EXP2,EXP3)	replace(exp1,exp2,exp3)

 

二、测试过程

日期函数

days(outworkdate) 函数转换*****************************************************************************
create table employee(id serial primary key,name varchar(100),outworkdate date);
insert into employee(name,outworkdate) values('alice','2023-01-15');    
insert into employee(name,outworkdate) values('bob','2023-02-20');
insert into employee(name,outworkdate) values('david','2023-04-05');
insert into employee(name,outworkdate) values('eve','2023-05-25');

testdb_0903=> select name,outworkdate,extract(epoch from outworkdate) / 86400 as days_since_epoch from employee;
 name  |     outworkdate     | days_since_epoch 
-------+---------------------+------------------
 alice | 2023-01-15 00:00:00 |            19372
 bob   | 2023-02-20 00:00:00 |            19408
 david | 2023-04-05 00:00:00 |            19452
 eve   | 2023-05-25 00:00:00 |            19502
(4 rows)

testdb_0903=> select name,outworkdate,extract(day from (outworkdate-date '1970-01-01'+integer '1'))  as days_since_epoch from employee;
 name  |     outworkdate     | days_since_epoch 
-------+---------------------+------------------
 alice | 2023-01-15 00:00:00 |            19373
 bob   | 2023-02-20 00:00:00 |            19409
 david | 2023-04-05 00:00:00 |            19453
 eve   | 2023-05-25 00:00:00 |            19503
(4 rows)

day(outworkdate) 函数转换*****************************************************************************
testdb_0903=> select name,outworkdate,extract(day from outworkdate)  as day_of_month from employee;
 name  |     outworkdate     | day_of_month 
-------+---------------------+--------------
 alice | 2023-01-15 00:00:00 |           15
 bob   | 2023-02-20 00:00:00 |           20
 david | 2023-04-05 00:00:00 |            5
 eve   | 2023-05-25 00:00:00 |           25
(4 rows)

testdb_0903=> 
testdb_0903=> 
testdb_0903=> select name,outworkdate,date_part('DAY',outworkdate) as day_of_month from employee;
 name  |     outworkdate     | day_of_month 
-------+---------------------+--------------
 alice | 2023-01-15 00:00:00 |           15
 bob   | 2023-02-20 00:00:00 |           20
 david | 2023-04-05 00:00:00 |            5
 eve   | 2023-05-25 00:00:00 |           25
(4 rows)

month(current_date) 函数转换*****************************************************************************
testdb_0903=> select extract(month from current_date) from dual;
 date_part 
-----------
         9
(1 row)

testdb_0903=> select date_part('MONTH',trunc(current_date)) from dual;
 date_part 
-----------
         9
(1 row)

year(current_date) 函数转换*****************************************************************************
testdb_0903=> select extract(year from current_date) from dual;
 date_part 
-----------
      2024
(1 row)

testdb_0903=> 
testdb_0903=> select date_part('YEAR',trunc(current_date)) from dual;
 date_part 
-----------
      2024
(1 row)

current_date -1 DAY/MONTH/YEAR 函数转换*****************************************************************************
testdb_0903=> select current_date as today,
current_date - interval '1 day' as yesterday,
current_date - interval '1 month' as last_month,
current_date - interval '1 year' as last_year from dual;
   today    |      yesterday      |     last_month      |      last_year      
------------+---------------------+---------------------+---------------------
 2024-09-29 | 2024-09-28 00:00:00 | 2024-08-29 00:00:00 | 2023-09-29 00:00:00
(1 row)

testdb_0903=> 
testdb_0903=> select trunc(current_date) - interval '1 DAY' as yesterday,
trunc(current_date) - interval '1 month' as last_month,
trunc(current_date) - interval '1 year' as last_year from dual;
      yesterday      |     last_month      |      last_year      
---------------------+---------------------+---------------------
 2024-09-28 00:00:00 | 2024-08-29 00:00:00 | 2023-09-29 00:00:00
(1 row)

current_date -1 DAY -1 MONTH 函数转换*****************************************************************************
testdb_0903=> select current_date - interval '1 DAY' - interval '1 MONTH' as result_date from dual;
     result_date     
---------------------
 2024-08-28 00:00:00
(1 row)

testdb_0903=> 
testdb_0903=> select trunc(current_date) - interval '1 DAY' - interval '1 MONTH' as result_date from dual;
     result_date     
---------------------
 2024-08-28 00:00:00
(1 row)

to_char(current_date,'yyyy-mm') 函数转换*****************************************************************************
testdb_0903=> select to_char(current_date,'yyyy-mm') from dual;
 to_char 
---------
 2024-09
(1 row)

testdb_0903=> select to_char(trunc(current_date),'yyyy-mm') from dual;
 to_char 
---------
 2024-09
(1 row)

timestampdiff(2,end_time-start_time) 函数转换*****************************************************************************
GaussDB同名函数仅在MySQL模式数据库中有效。
testdb_0903=> create table events(id serial primary key,start_time timestamp,end_time timestamp);
testdb_0903=> insert into events(start_time,end_time) values('2023-10-01 10:00:00','2023-10-01 10:30:00');
testdb_0903=> insert into events(start_time,end_time) values('2023-10-01 11:00:00','2023-10-01 12:15:00');
testdb_0903=> insert into events(start_time,end_time) values('2023-10-01 13:00:00','2023-10-01 13:45:00');


testdb_0903=> select id,start_time,end_time,extract(epoch from (end_time - start_time))  as diff_time from events;
 id |     start_time      |      end_time       | diff_time 
----+---------------------+---------------------+-----------
  1 | 2023-10-01 10:00:00 | 2023-10-01 10:30:00 |      1800
  2 | 2023-10-01 11:00:00 | 2023-10-01 12:15:00 |      4500
  3 | 2023-10-01 13:00:00 | 2023-10-01 13:45:00 |      2700
(3 rows)

testdb_0903=> 
testdb_0903=> select id,start_time,end_time,trunc(extract(epoch from (end_time - start_time))) as diff_time from events;
 id |     start_time      |      end_time       | diff_time 
----+---------------------+---------------------+-----------
  1 | 2023-10-01 10:00:00 | 2023-10-01 10:30:00 |      1800
  2 | 2023-10-01 11:00:00 | 2023-10-01 12:15:00 |      4500
  3 | 2023-10-01 13:00:00 | 2023-10-01 13:45:00 |      2700
(3 rows)

 

数据类型转化

dec(RATE,10,2) 函数转换*****************************************************************************
create table sales(id serial primary key,rate float);
insert into sales(rate) values(123.456),(789.123456),(456.789),(12.3),(0.987654);

testdb_0903=> select id,rate,rate::numeric(10,2) as formatted_rate from sales;
 id |        rate         | formatted_rate 
----+---------------------+----------------
  1 | 123.456000000000003 |         123.46
  2 | 789.123456000000033 |         789.12
  3 | 456.788999999999987 |         456.79
  4 | 12.3000000000000007 |          12.30
  5 | .987654000000000032 |            .99
(5 rows)

testdb_0903=> 
testdb_0903=> 
testdb_0903=> select id,rate,cast(rate as numeric(10,2)) as formatted_rate from sales;
 id |        rate         | formatted_rate 
----+---------------------+----------------
  1 | 123.456000000000003 |         123.46
  2 | 789.123456000000033 |         789.12
  3 | 456.788999999999987 |         456.79
  4 | 12.3000000000000007 |          12.30
  5 | .987654000000000032 |            .99
(5 rows)


int(100.123) 函数转换*****************************************************************************
testdb_0903=> select cast(100.123 as int) as int_value from dual;
 int_value 
-----------
       100
(1 row)

testdb_0903=> 
testdb_0903=> select 100.123::int as int_values from dual;
 int_values 
------------
        100
(1 row)

char(1) 函数转换*****************************************************************************
testdb_0903=> select cast(1 as char(1)) as char_value;
 char_value 
------------
 1
(1 row)


to_char(1) 函数转换*****************************************************************************
testdb_0903=> select to_char(current_timestamp,'HH12:MI:SS');
 to_char  
----------
 10:14:46
(1 row)

testdb_0903=> select to_char(125.8::real,'999D99');
 to_char 
---------
  125.80
(1 row)


to_date(1) 函数转换*****************************************************************************
testdb_0903=> select to_date('2024-09-30');
       to_date       
---------------------
 2024-09-30 00:00:00
(1 row)

testdb_0903=> select to_date('05 Dec 2000','DD Mon YYYY');
       to_date       
---------------------
 2000-12-05 00:00:00
(1 row)

 

其它常用函数转换

locate('|','115|56',1) 函数转换*****************************************************************************

testdb_0903=> select instr('115|56','|',1) as position from dual;
 position 
----------
        4
(1 row)


listagg(name,',') 函数转换*****************************************************************************
testdb_0903=> create table listagg_t1(a int,b text);
testdb_0903=> insert into listagg_t1 values(null,'a1'),(1,'b2'),(1,'c3'),(2,'d4'),(2,'e5'),(3,'f6');

testdb_0903=> select a,listagg(b,';') within group (order by b)  from listagg_t1 group by 1;
 a | listagg 
---+---------
 1 | b2;c3
 2 | d4;e5
 3 | f6
   | a1
(4 rows)

nvl() 函数转换*****************************************************************************
testdb_0903=> select nvl(null,1);
 nvl 
-----
 1
(1 row)

testdb_0903=> 
testdb_0903=> select nvl('Hello world',1);
     nvl     
-------------
 Hello world
(1 row)


trim() 函数转换*****************************************************************************
testdb_0903=> select trim(BOTH 'x' from 'xTommxx');
 btrim 
-------
 Tomm
(1 row)

testdb_0903=> select trim(leading 'x' from 'xTommxx');
 ltrim  
--------
 Tommxx
(1 row)

testdb_0903=> select trim(trailing 'x' from 'xTommxx');
 rtrim 
-------
 xTomm
(1 row)

substr() 函数转换*****************************************************************************
testdb_0903=> 
testdb_0903=> select substr('stringtest' from 4);
 substr  
---------
 ingtest
(1 row)

testdb_0903=> select substr('stringtest',4);
 substr  
---------
 ingtest
(1 row)

testdb_0903=> 
testdb_0903=> select substr('teststring' from 5 for 2);
 substr 
--------
 st
(1 row)

testdb_0903=> select substr('string',2,3);
 substr 
--------
 tri
(1 row)

value() 函数转换*****************************************************************************
testdb_0903=> select coalesce(null,'hello');
 coalesce 
----------
 hello
(1 row)

floor() 函数转换*****************************************************************************
testdb_0903=> select floor(-42.8);
 floor 
-------
   -43
(1 row)

round() 函数转换*****************************************************************************
testdb_0903=> select round(42.4);
 round 
-------
    42
(1 row)

coalesce() 函数转换*****************************************************************************
testdb_0903=> select coalesce(null,'hello');
 coalesce 
----------
 hello
(1 row)

length() 函数转换*****************************************************************************
testdb_0903=> select length('abcd');
 length 
--------
      4
(1 row)

testdb_0903=> 
testdb_0903=> select length('汉字abc');
 length 
--------
      5
(1 row)

posstr(exp1,exp2) 函数转换*****************************************************************************

testdb_0903=> select position('World' in 'Hello World') as pos;
 pos 
-----
   7
(1 row)

replace() 函数转换*****************************************************************************
testdb_0903=> select replace('abcdefabcdef','cd','XXX');
    replace     
----------------
 abXXXefabXXXef
(1 row)

testdb_0903=> select replace('abcdefabcdef','cd');
 replace  
----------
 abefabef
(1 row)