1.instr函数可以用like替换
也可以用 POSITION (\'试油\' in T1.WELLTESTMETHOD)>0替换
2.decode可以用case when 2 then 2 when 1 then -1替换
SELECT
M.DESIGN_ID,
MAX( DECODE( M.AUDIT_CODE, 2, 2, 1,- 1, 0, 0 ) ) AUDIT_CODE
FROM
PC_BUILD_DAILY_REPORT_DAY M
WHERE
to_date ( m.control_date, \'yyyy-mm-dd\' ) = to_date ( \'2019-05-21\', \'yyyy-mm-dd\' )
GROUP BY
M.DESIGN_ID
SELECT
A.design_id,
MAX(
CASE A.AUDIT_CODE
WHEN \'2\' THEN \'2\'
WHEN \'1\' THEN \'-1\'
WHEN \'0\' THEN \'0\'
END) AS AUDIT_CODE
FROM PC_BUILD_DAILY_REPORT_DAY A
WHERE
to_date ( A.control_date, \'yyyy-mm-dd\' ) = to_date ( \'2019-05-21\', \'yyyy-mm-dd\' )
GROUP BY
A.DESIGN_ID
3.SUBSTR 截取字符串的开始位置必须为1 例如截取aaaaa的四位 SUBSTR (\'aaaaa\',1,4) 若为SUBSTR (\'aaaaa\',0,4) 则无效
4.PostgreSQL中不需要dual虚拟表 select语句可以没有from
5.类似于select *from(select...) from里面的子查询必须要起别名,多层嵌套一样都要起别名
如select *from(select *from(select...) as A)as B
6.postgre中没有trunc、addmonths、lastday函数可以用date_trunc、interval替代(已经编写了f_add_months f_last_day函数可用)
例子：
求日期该年第一天
trunc(TO_DATE(\'20190714\', \'yyyymmdd\'),\'yyyy\')
date_trunc(\'year\',TO_DATE(\'20190714\', \'yyyymmdd\'))
求日期该年最后一天 两种方式替换（第二种比较好）
last_day(add_months(trunc(TO_DATE(\'20190714\', \'yyyymmdd\'),\'y\'),11))
date_trunc(\'day\',(date_trunc(\'year\',TO_DATE(\'20190714\', \'yyyymmdd\'))+ interval \'11 month\')+interval \'30 day\')
(date_trunc(\'MONTH\',date_trunc(\'year\',TO_DATE(\'2019-07-14\', \'yyyy-mm-dd\'))+ interval \'11 month\') + INTERVAL \'1 MONTH - 1 day\')
求日期该月第一天
TRUNC(TO_DATE(\'20190414\', \'yyyymmdd\'),\'mm\')
TRUNC(ADD_MONTHS(LAST_DAY(TO_DATE(\'20190414\', \'yyyymmdd\')),-1)) + 1
date_trunc(\'MONTH\',(date_trunc(\'MONTH\',to_date(\'2019-07-09\',\'yyyy-mm-dd\')) - INTERVAL \'1 MONTH\')+ INTERVAL \'1 MONTH\')
详细介绍见https://blog.csdn.net/liguangxianbin/article/details/80166574
7.postgre中没有nvl函数，可以用coalesce函数替代
nvl(collect_result,0) as collect_result
coalesce(collect_result,0) as collect_result
8.字符串去掉空格
oracle
Select LTRIM(\' sql_in_a_nutshell\'),
Select RTRIM(\'sql_in_a_nutshell \'),
TRIM(\' sql_in_a_nutshell \')
FROM dual;
PostgreSQL
Select TRIM(LEADING FROM \' sql_in_a_nutshell\'),
TRIM(TRAILING FROM \'sql_in_a_nutshell \'),
TRIM(BOTH FROM \' sql_in_a_nutshell \');
9.上面清除空格相反的操作，添加空格
oracle
Select LPAD((\'sql\', 5, \' \'),
RPAD((\'sql\', 5, \' \')
FROM dual;
PostgreSQL
Select LPAD(\'sql\', 5, \' \'),
LPAD(\'sql\', 2, \' \'),
RPAD(\'sql\', 5, \' \'),
RPAD(\'sql\', 2, \' \'),;
//结果为 \' sql\' \'sq\' \'sql \' \'ql\'
10.字符串替换
oracle
Select
REPLACE(\'wabbit_season\',\'it_\',\'it_hunting_\')
FROM dual;
PostgreSQL
Select TRANSLATE(\'wabbit_season\',\'it_\',\'it_hunting_\');
Select replace(\'wabbit_season\',\'it_\',\'it_hunting_\');
11.NULLIF(expression1, expression2) 如果 expression1 等于 expression2则返回 NULL，如果expression1的值为null,也返回NULL
oracle
Select DECODE(foo,\'Wabbits!\',NULL)
FROM dual;
PostgreSQL
Select NULLIF(foo, \'Wabbits!\');
12.postgre中没有nvl2函数，可以用case when is not null then 2 else 1替换
nvl2(name, \'有人\', \'无人\')
when name is not null then \'有人\' else \'无人\' end
13 REGEXP_SUBSTR可以替换为substring (匹配正则表达式)
REGEXP_SUBSTR(ST.STRAT_UNIT_NAME,\'[^\'|| UNISTR(\'\4e00\') ||\'-\'||UNISTR(\'\9fa5\') || \']\',1,1)
SELECT substring(ST.STRAT_UNIT_NAME from \'[^\u4e00-\u9fa5]\')
14 postgre函数学习手册https://blog.csdn.net/zdq0394123/article/details/8227567
15 FNSPLIT 可以用regexpsplittotable替换(列转行)
SELECT split_part(\'哈-哈哈哈\', \'哈\', 2) //结果 -
SELECT substring(\'你好-哈哈\' from \'([\u3007\u3400-\u4DB5\u4E00-\u9FCB\uF900-\uFA2D]+-)\')//结果 你好-
SELECT a.string_to_array[2] from (SELECT string_to_array (\'a,b,b\',\',\')) as a //结果b
SELECT split_part(\'accb\',\'c\',2) //无结果
SELECT regexp_split_to_table(\'a,b,b\',\',\')//结果a b b集合
16(行转列)
PIVOT(MAX(BTM_DEPTH) BTM_DEPTH,(MAX(BTM_DEPTH - TOP_DEPTH)) THICKNESS, MAX(OIL_GAS_POSITION) OIL_GAS_POSITION, MAX(DIP_ANGLE) DIP_ANGLE
FOR PHASE IN(\'设计\' DESIGN, \'实际\' ACTUAL))
max( CASE WHEN PHASE = \'设计\' THEN BTM_DEPTH ELSE 0 END ) AS DESIGN_BTM_DEPTH,
max( CASE WHEN PHASE = \'实际\' THEN BTM_DEPTH ELSE 0 END ) AS ACTUAL_BTM_DEPTH,
max( CASE WHEN PHASE = \'设计\' THEN BTM_DEPTH - TOP_DEPTH ELSE 0 END ) AS DESIGN_THICKNESS,
max( CASE WHEN PHASE = \'实际\' THEN BTM_DEPTH - TOP_DEPTH ELSE 0 END ) AS ACTUAL_THICKNESS,
max( CASE WHEN PHASE = \'设计\' THEN OIL_GAS_POSITION ELSE \'\' END ) AS DESIGN_OIL_GAS_POSITION,
max( CASE WHEN PHASE = \'实际\' THEN OIL_GAS_POSITION ELSE \'\' END ) AS ACTUAL_OIL_GAS_POSITION,
max( CASE WHEN PHASE = \'设计\' THEN DIP_ANGLE ELSE 0 END ) AS DESIGN_DIP_ANGLE,
max( CASE WHEN PHASE = \'实际\' THEN DIP_ANGLE ELSE 0 END ) AS ACTUAL_DIP_ANGLE
17 postgre对于数据类型的要求十分严格,并且没有自动转换格式,而oracle对于数据类型要求不是十分严格
例如用||拼接字符串的时候 \'aaa\'||123||\'bbb\' 这种就会报错(oracle不会报错,正常运行) 需要改为 \'aaa\'||to_char(123,\'99999999999\')||\'bbb\' 才能拼接 ,
需要编写者自行匹配正确的数据格式,如果格式不相符,则需要用to_char(字段,\'999999999999\')或to_number(字段,\'9999999999999999\') 或cast(字段 as varchar) cast(字段 as integer)
PS:
对于to_char 9的数量没有限制,尽量多些,不然会丢失结果,
如to_char(123,\'9\') 结果为 \' #\';
to_char(123,\'99\') 结果为 \' ##\';
to_char(123,\'999\') 结果为 \' 123\'
to_char(123,\'9999\') 结果为 \' 123\'
随着9的增加 123前面的空格增多,但并不影响计算
对于to_number 9的数量没有限制,尽量多些,不然会丢失位数,
如to_number(\'123\',\'9\') 结果为 1;
to_number(\'123\',\'99\') 结果为 12;
to_number(123,\'999\') 结果为 123
to_char(123,\'9999\') 结果为 123 随着9的增加 结果始终是123
18 贼实用的generate_series函数
|
函数 |
参数类型 |
返回类型 |
描述 |
|
generate_series(start, stop) |
int 或 bigint |
setof int 或 setof bigint(与参数类型相同) |
生成一个数值序列，从start 到 stop，步进为一 |
|
generate_series(start, stop, step) |
int 或 bigint |
setof int 或 setof bigint(与参数类型相同) |
生成一个数值序列，从start 到 stop，步进为step |
|
generate_series(start, stop, step_interval) |
timestamp or timestamp with time zone |
timestamp 或 timestamp with time zone(same as argument type) |
生成一个数值序列，从start 到 stop，步进为step |
SELECT generate_series(1,5,2)
结果
1
3
5
select date(zz) as t from generate_series(date_trunc(\'month\',to_date(\'201505\',\'yyyymm\')), date_trunc(\'month\',to_date(\'201507\',\'yyyymm\')),\'1 month\') as zz;
结果
2015-05-01
2015-06-01
2015-07-01
19 新增fn_get_month_days函数,获取当月天数
例子:
select fn_get_month_days(\'201912\')
结果 31
20 替代Oracle中ALL_TAB_COLUMNS与ALL_TABLES
ALL_TAB_COLUMNS:
SELECT
col_description ( A.attrelid, A.attnum ) AS COMMENT,
format_type ( A.atttypid, A.atttypmod ) AS TYPE,
A.attname AS NAME,
A.attnotnull AS NOTNULL
FROM
pg_class AS C,
pg_attribute AS A
WHERE
C.relname = \'cd_well\'
AND A.attrelid = C.oid
AND A.attnum > 0
ALL_TABLES:
SELECT
relname AS tabname,
CAST ( obj_description ( relfilenode, \'pg_class\' ) AS VARCHAR ) AS COMMENT
FROM
pg_class C
WHERE
relkind = \'r\'
AND relname NOT LIKE\'pg_%\'
AND relname NOT LIKE\'sql_%\'
ORDER BY
relname
21 ‘a’ || null=？
Oracle中 ‘a’ || null = ‘a’
Postgre中 ‘a’ || null = null