不一样，仔细看看这个：You use the VARCHAR2 datatype to store variable-length character data. How the data is represented internally depends on the database character set. The VARCHAR2 datatype takes a required parameter that specifies a maximum size up to 32767 bytes. The syntax follows:VARCHAR2(maximum_size [CHAR | BYTE])You cannot use a symbolic constant or variable to specify the maximum size; you must use an integer literal in the range 1 .. 32767.Small VARCHAR2 variables are optimized for performance, and larger ones are optimized for efficient memory use. The cutoff point is 2000 bytes. For a VARCHAR2 that is 2000 bytes or longer, PL/SQL dynamically allocates only enough memory tohold the actual value. For a VARCHAR2 variable that is shorter than 2000 bytes,PL/SQL preallocates the full declared length of the variable. For example, if you assign the same 500-byte value to a VARCHAR2(2000 BYTE) variable and to a VARCHAR2(1999 BYTE) variable, the former takes up 500 bytes and the latter takes up 1999 bytes.
Small VARCHAR2 variables are optimized for performance, and larger ones are optimized for efficient memory use. The cutoff point is 2000 bytes. For a VARCHAR2 that is 2000 bytes or longer, PL/SQL dynamically allocates only enough memory to hold the actual value. For a VARCHAR2 variable that is shorter than 2000 bytes, PL/SQL preallocates the full declared length of the variable. For example, if you assign the same 500-byte value to a VARCHAR2(2000 BYTE) variable and to a VARCHAR2(1999 BYTE) variable, the former takes up 500 bytes and the latter takes up 1999 bytes 在2000的时候有一个区分，〉2000的动态分配，有多大，分配多大，小于2000的，eg varchar2(1999),就分配1999
data is represented internally depends on the database character set. The VARCHAR2
datatype takes a required parameter that specifies a maximum size up to 32767
bytes. The syntax follows:VARCHAR2(maximum_size [CHAR | BYTE])You cannot use a symbolic constant or variable to specify the maximum size; you
must use an integer literal in the range 1 .. 32767.Small VARCHAR2 variables are optimized for performance, and larger ones are
optimized for efficient memory use. The cutoff point is 2000 bytes. For a VARCHAR2
that is 2000 bytes or longer, PL/SQL dynamically allocates only enough memory tohold the actual value. For a VARCHAR2 variable that is shorter than 2000 bytes,PL/SQL preallocates the full declared length of the variable. For example, if you assign the same 500-byte value to a VARCHAR2(2000 BYTE) variable and to a VARCHAR2(1999 BYTE) variable, the former takes up 500 bytes and the latter takes up 1999 bytes.
在2000的时候有一个区分，〉2000的动态分配，有多大，分配多大，小于2000的，eg varchar2(1999),就分配1999