Oracle basic data type --- (string)

Oracle string format
 
First, we will introduce the char (N) and Varchar2 (N) formats.
Create table TEST_CHAR
(
CHAR_COL CHAR (10 ),
VARCHAR_COL VARCHAR2 (10 ),
);
SQL> insert into test_char (char_col, varchar_col) values ('20140901', '20160901 ');
SQL> commit;
SQL> select char_col, dump (char_col, 16) as d_char_col, varchar_col, dump (varchar_col, 16) as d_varchar_col from test_char;
 
CHAR_COL D_CHAR_COL VARCHAR_COL D_VARCHAR_COL
---------- Certificate -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
123 Typ = 96 Len = 10: 31,32, 33,20, 20,20, 20,20, 20,20 123 Typ = 1 Len = 3: 31,32, 33
 
As you can see, the char type is automatically followed by spaces if the length is not enough. For the varchar type, only '123' is stored '.
SQL> select to_number ('31', 'xx') from dual;
 
TO_NUMBER ('31', 'xx ')
--------------------
49
---- First, convert the hexadecimal data into a hexadecimal data.
SQL> select chr (49) from dual;
 
CHR (49)
-------
1
Get 49 characters.
Summary: oracle stores characters, which are converted to the corresponding ASCII code for storage.
 
SQL> insert into test_char (char_col, varchar_col) values ('Magic status', 'Magic status ');
SQL> commit;
 
Commit complete
 
SQL> select char_col, dump (char_col, 16) as d_char_col, varchar_col, dump (varchar_col, 16) as d_varchar_col from test_char;
 
CHAR_COL D_CHAR_COL VARCHAR_COL D_VARCHAR_COL
---------- Certificate -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
123 Typ = 96 Len = 10: 31,32, 33,20, 20,20, 20,20, 20,20 123 Typ = 1 Len = 3: 31,32, 33
Magic country Typ = 96 Len = 10: c9, f1, c6, e6, b5, c4, b9, fa, bc, d2 magic country Typ = 1 Len = 10: c9, f1, c6, e6, b5, c4, b9, fa, bc, d2
We can see that Chinese characters are stored in two bytes.
 
Next we will introduce NChar (N) and NVarchar2 (N ).
 
Create table TEST_NCHAR
(
CHAR_COL NCHAR (10 ),
VARCHAR_COL NVARCHAR2 (10)
);
 
 
SQL> insert into test_nchar (char_col, VARCHAR_COL) values ('20140901', '20160901 ');
 
1 row inserted
 
SQL> commit;
 
Commit complete
 
SQL> select char_col, dump (char_col, 16) as d_char_col, VARCHAR_COL, dump (VARCHAR_COL, 16) as d_VARCHAR_COL from test_nchar;
 
CHAR_COL D_CHAR_COL VARCHAR_COL D_VARCHAR_COL
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
123 Typ = 96 Len = 20: 123 31, 32, 33, 20, Typ = 1 Len = 6 :,
 
We can clearly see that the string '123456' is inserted at the same time, but the NChar is 0, 31, 123, that is to say: the high value is supplemented with 0 to supplement two bytes.
Summary: NChar and Nvarchar2 store all characters in two bytes.
The four types of characters and numbers are stored in ASCII codes.
You can view the character set of oracle:
SQL> select * from sys. props $ where name like '% CHARACTERSET % ';
 
Name value $ COMMENT $
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
NLS_CHARACTERSET ZHS16GBK Character set
NLS_NCHAR_CHARACTERSET AL16UTF16 NCHAR Character set