SQL经典案例之不同数据库对字符串顺序排列字符

问题描述

将字符串按照字符顺序从左到右进行排序

--排序前-- >>>> ---排序后---
OLD_NAME        NEW_NAME
--------- >>>> ----------
DB2             2BD
GAUSSDB         ABDGSSU
MONGODB         BDGMNOO
MYSQL           LMQSY
ORACLE          ACELOR
POSTGRESQL      EGLOPQRSST
SQLSERVER       EELQRRSSV
TIDB            BDIT
--------- >>>> ----------

处理逻辑：先将字符串拆分成单个字符，再将各个字符按所在字符串（分组）进行排序

构造测试数据

drop table t_string;
create table t_string(tid int,tname varchar(10));
insert into t_string values(1,'ORACLE');
insert into t_string values(2,'MYSQL');
insert into t_string values(3,'POSTGRESQL');
insert into t_string values(4,'SQLSERVER');
insert into t_string values(5,'DB2');
insert into t_string values(6,'GAUSSDB');
insert into t_string values(7,'TIDB');
insert into t_string values(8,'MONGODB');

-- tid的个数需要 >= tname列的数据最大长度
drop table t_10;
create table t_10(tid int);
insert into t_10 values(1);
insert into t_10 values(2);
insert into t_10 values(3);
insert into t_10 values(4);
insert into t_10 values(5);
insert into t_10 values(6);
insert into t_10 values(7);
insert into t_10 values(8);
insert into t_10 values(9);
insert into t_10 values(10);

commit;

Oracle

函数 SYS_CONNECT_BY_PATH 能以迭代的方式创建列表，主要用于树查询(层次查询) 以及多列转行，其语法一般为：

select ... sys_connect_by_path(column_name,'connect_symbol') from table 
start with ... connect by ... prior

完整语句：取分组长度一致的那个数据即排好序的字符串

col old_name format a15
col new_name format a15

select old_name, new_name
from (
select old_name,replace(sys_connect_by_path(c,' '),' ') as new_name
from (
	select t.tname as old_name,
	row_number() over(partition by t.tname order by substr(t.tname,iter.pos,1)) rn,
	substr(t.tname,iter.pos,1) c
	from t_string t,
	(select rownum as pos from t_10) iter 
	where iter.pos <= length(t.tname) order by 1
) x
start with rn = 1
connect by prior rn = rn-1 and prior old_name = old_name
) where length(old_name) = length(new_name);

拆解：将拆分的单个字符排序拼接起来

select old_name,replace(sys_connect_by_path(c,' '),' ') as new_name
from (
	select t.tname as old_name,
	row_number() over(partition by t.tname order by substr(t.tname,iter.pos,1)) rn,
	substr(t.tname,iter.pos,1) c
	from t_string t,
	(select rownum as pos from t_10) iter 
	where iter.pos <= length(t.tname) order by 1
) x
start with rn = 1
connect by prior rn = rn-1 and prior old_name = old_name;

拆解：最内层，按row_number排序拆分字符串为单个字符

	select t.tname as old_name,
	row_number() over(partition by t.tname order by substr(t.tname,iter.pos,1)) rn,
	substr(t.tname,iter.pos,1) c
	from t_string t,
	(select rownum as pos from t_10) iter 
	where iter.pos <= length(t.tname) order by 1;

MySQL

GROUP_CONCAT：不仅能进行拼接，还能进行排序，默认逗号分隔，可用separator指定分隔符，语法如下：

group_concat([DISTINCT] 要连接的字段 [Order BY ASC/DESC 排序字段] [Separator '分隔符'])

完整语句：将拆分的字符排序后进行拼接

select tname as old_name,group_concat(c order by c separator '') as new_name 
from(
	select tname,substr(t.tname,iter.pos,1) c
	from t_string t,
	(select tid as pos from t_10) iter 
	where iter.pos <= length(t.tname)
) x 
group by tname;

拆解：将字符串拆分成单个字符（乱序）

	select tname,substr(t.tname,iter.pos,1) c
	from t_string t,
	(select tid as pos from t_10) iter 
	where iter.pos <= length(t.tname);

PostgreSQL

STRING_AGG：对字符串进行排序

select tname as old_name,string_agg(c,'' order by c) as new_name 
from (
	select t.tname,substr(t.tname,iter.pos,1) as c
	from t_string t,
	(select tid as pos from t_10) iter 
	where iter.pos <= length(t.tname)
	order by 1,2
) x
group by tname;

拆解：将字符串拆分成单个字符再进行排序

	select t.tname,substr(t.tname,iter.pos,1) as c
	from t_string t,
	(select tid as pos from t_10) iter 
	where iter.pos <= length(t.tname)
	order by 1,2;