Oracle characterset, char semantics & storage length

[oracle@oracle19c admin]$ sql donghua@orclpdb

SQLcl: Release 19.1 Production on Fri Oct 18 23:03:04 2019

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Last Successful login time: Fri Oct 18 2019 23:03:08 +08:00

Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0

SQL> select /*ansiconsole*/ * from nls_database_parameters where parameter like '%CHARACTERSET%';
PARAMETER                VALUE       
NLS_NCHAR_CHARACTERSET   AL16UTF16   
NLS_CHARACTERSET         AL32UTF8    


SQL> create table t1 (c1 varchar2(20 byte), c2 varchar2(20 char), c3 nvarchar2(20));

Table created.

SQL> desc t1;

Name                 Null?    Type                        
-------------------- -------- ----------------------------
C1                            VARCHAR2(20)                
C2                            VARCHAR2(20 CHAR)     
C3                            NVARCHAR2(20)      

SQL> insert into t1 values ('a','a','a');

1 row created.

SQL> insert into t1 values ('中','中','中');

1 row created.

SQL> commit;

Commit complete.

SQL> select /*ansiconsole*/ * from t1;

C1                   C2                   C3                  
-------------------- -------------------- --------------------
a                    a                    a                   
中                    中                    中                   

SQL> select /*ansiconsole*/ length(c1),length(c2),length(c3) from t1;

LENGTH(C1) LENGTH(C2) LENGTH(C3)
---------- ---------- ----------
         1          1          1
         1          1          1

SQL> select /*ansiconsole*/ lengthb(c1),lengthb(c2),lengthb(c3) from t1;

LENGTHB(C1) LENGTHB(C2) LENGTHB(C3)
----------- ----------- -----------
          1           1           2
          3           3           2


SQL> update t1 set c1='中中中中中中';

2 rows updated.

SQL> update t1 set c1='中中中中中中中';

update t1 set c1='中中中中中中中'
                 *
ERROR at line 1:
ORA-12899: value too large for column "DONGHUA"."T1"."C1" (actual: 21, maximum: 20)



SQL> update t1 set c2='中中中中中中中中中中中中中中中中中中中中';

2 rows updated.

SQL> update t1 set c2='中中中中中中中中中中中中中中中中中中中中中';

update t1 set c2='中中中中中中中中中中中中中中中中中中中中中'
                 *
ERROR at line 1:
ORA-12899: value too large for column "DONGHUA"."T1"."C2" (actual: 21, maximum: 20)



SQL> update t1 set c3='中中中中中中中中中中中中中中中中中中中中';

2 rows updated.

SQL> update t1 set c3='中中中中中中中中中中中中中中中中中中中中中';

update t1 set c3='中中中中中中中中中中中中中中中中中中中中中'
                 *
ERROR at line 1:
ORA-12899: value too large for column "DONGHUA"."T1"."C3" (actual: 21, maximum: 20)