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)