VARCHAR2 Data TypeThe VARCHAR2 data type specifies a variable-length character string. When you create a VARCHAR2 column, you supply the maximum number of bytes or characters of data that it can hold. Oracle subsequently stores each value in the column exactly as you specify it, provided the value does not exceed the column's maximum length of the column. If you try to insert a value that exceeds the specified length, then Oracle returns an error.You must specify a maximum length for a VARCHAR2 column. This maximum must be at least 1 byte, although the actual string stored is permitted to be a zero-length string (''). You can use the CHAR qualifier, for example VARCHAR2(10 CHAR), to give the maximum length in characters instead of bytes. A character is technically a code point of the database character set. You can use the BYTE qualifier, for example VARCHAR2(10 BYTE), to explicitly give the maximum length in bytes. If no explicit qualifier is included in a column or attribute definition when a database object with this column or attribute is created, then the length semantics are determined by the value of the NLS_LENGTH_SEMANTICS parameter of the session creating the object. Independently of the maximum length in characters, the length of VARCHAR2 data cannot exceed 4000 bytes. Oracle compares VARCHAR2 values using nonpadded comparison semantics.

SQL> select * from v$version t where rownum<2;BANNER
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Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit ProductionSQL> select * from v$nls_parameters t where t.PARAMETER='NLS_LENGTH_SEMANTICS';PARAMETER                                                        VALUE
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NLS_LENGTH_SEMANTICS                                             BYTESQL>

create table test_varchar2_datatype(
char_1 varchar2(4000 byte),
char_2 varchar2(4000 char),
char_3 varchar2(4000),
char_21 varchar2(2000 byte),
char_22 varchar2(2000 char),
char_23 varchar2(2000)
);

SQL> select length(listagg(t.username) within group (order by t.userid)||'中国石化') from t_char_source t2  where rownum <148;LENGTH(LISTAGG(T.USERNAME)WITHINGROUP(ORDERBYT.USERID)||'中国石化')
-------------------------------------------------------------------2000SQL> insert into test_varchar2_datatype(char_1,2                                     char_2,3                                     char_3,4                                     char_21,5                                     char_22,6                                     char_237                                     )8  select9  listagg(t.username) within group (order by t.userid)||'中国石化',10  listagg(t.username) within group (order by t.userid)||'中国石化',11  listagg(t.username) within group (order by t.userid)||'中国石化',12  listagg(t.username) within group (order by t.userid)||'中国石化',13  listagg(t.username) within group (order by t.userid)||'中国石化',14  listagg(t.username) within group (order by t.userid)||'中国石化'15  from t_char_source t16  where rownum <148;
listagg(t.username) within group (order by t.userid)||'中国石化',*
第 12 行出现错误:
ORA-12899: 列 "HR"."TEST_VARCHAR2_DATATYPE"."CHAR_21" 的值太大 (实际值: 3991, 最大值: 2000)SQL> insert into test_varchar2_datatype(char_1,2                                     char_2,3                                     char_3,4                                     char_22,5                                     char_236                                     )7  select8  listagg(t.username) within group (order by t.userid)||'中国石化',9  listagg(t.username) within group (order by t.userid)||'中国石化',10  listagg(t.username) within group (order by t.userid)||'中国石化',11  listagg(t.username) within group (order by t.userid)||'中国石化',12  listagg(t.username) within group (order by t.userid)||'中国石化'13  from t_char_source t14  where rownum <148;
listagg(t.username) within group (order by t.userid)||'中国石化'*
第 12 行出现错误:
ORA-12899: 列 "HR"."TEST_VARCHAR2_DATATYPE"."CHAR_23" 的值太大 (实际值: 3991, 最大值: 2000)SQL> insert into test_varchar2_datatype(char_1,2                                     char_2,3                                     char_3,4                                     char_225                                     )6  select7  listagg(t.username) within group (order by t.userid)||'中国石化',8  listagg(t.username) within group (order by t.userid)||'中国石化',9  listagg(t.username) within group (order by t.userid)||'中国石化',10  listagg(t.username) within group (order by t.userid)||'中国石化'11  from t_char_source t12  where rownum <148;已创建 1 行。SQL> commit;SQL> select length(listagg(t.username) within group (order by t.userid)||'中国石化') from t_char_source t2  where rownum <150;
select length(listagg(t.username) within group (order by t.userid)||'中国石化') from t_char_source t*
第 1 行出现错误:
ORA-01489: 字符串连接的结果过长SQL>