OracleとPostgreSQL(+Redshift)のchar、varcharのバイトと文字数の違い

create table chartest(a char(10));

postgres> insert into chartest values('１２３４５６７８９あ');                                                                                                                              
INSERT 0 1
Time: 0.004s
postgres> SELECT LENGTH(a) from chartest;                                                                                                                                                   
+----------+
| length   |
|----------|
| 10       |
+----------+
SELECT 1
Time: 0.017s
postgres> SELECT OCTET_LENGTH(a) from chartest;                                                                                                                                             
+----------------+
| octet_length   |
|----------------|
| 30             |
+----------------+
SELECT 1
Time: 0.017s
#文字数オーバーなパターン
postgres> insert into chartest values('１２３４５６７８９あい');                                                                                                                            
value too long for type character(10)

Time: 0.004s
postgres>  

SQL> insert into chartest values('１２３');

1 row inserted.

SQL> SELECT LENGTHB(a) from chartest;
   LENGTHB(A) 
_____________ 
           10 


SQL> SELECT LENGTH(a) from chartest;
   LENGTH(A) 
____________ 
           4 


SQL> insert into chartest values('１２３４');

Error starting at line : 1 in command -
insert into chartest values('１２３４')
Error report -
ORA-12899: value too large for column "ADMIN"."CHARTEST"."A" (actual: 12, maximum: 10)