oraclevarchar多⼤,varchar2设置长度与实际⼤⼩以前有学⽣问过，varchar2(4k)与varchar2(1)⾥⾯存同样的数据会怎么样。
我喜欢直接⽤测试结果说话，现在把实验补上
CREATE TABLE vc1(c1 VARCHAR2(1));
CREATE TABLE vc4k(c1 VARCHAR2(4000));
分别加⼊1W⾏数据进去
SQL> insert into vc1 select * from vc4k;
1000000 rows inserted
SQL> select s.BYTES/1024/1024 from user_segments s where s.segment_name in(upper('vc4k'),upper('vc1'));
S.BYTES/1024/1024
-----------------
13
13
2 rows selected
SQL> select count(*) from vc1 union all select count(*) from vc4k;
COUNT(*)
----------
1000000
1000000
2 rows selected
SQL> select c.TABLE_NAME,c.COLUMN_NAME,c.DATA_TYPE,c.DATA_LENGTH from user_tab_columns c where c.TABLE_NAME in(upper('vc4k'),upper('vc1'));
TABLE_NAME COLUMN_NAM DATA_TYPE DATA_LENGTH
---------- ---------- ---------- -----------
VC1 C1 VARCHAR2 1
VC4K C1 VARCHAR2 4000
2 rows selected
SQL>
segment⼀样
varchar2最大长度
各⾃增加1W⾏再看。
SQL> insert into vc1 select * from vc4k;
1000000 rows inserted
SQL> insert into vc4k select * from vc4k;
1000000 rows inserted
SQL> select s.BYTES/1024/1024 from user_segments s where s.segment_name in(upper('vc4k'),upper('vc1')); S.BYTES/1024/1024
-----------------
25
25
2 rows selected
SQL> 仍然⼀样

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