【原创】【HCIA】验证GaussDB 100系统函数to_nchar()是否能支持最大字节长度8000

在华为HCIA GaussDB 100的资料中，遇到一个这样的内容：函数to_nchar()返回值是否支持最大8000字节。

为验证实际情况，进行以下实验（环境：GaussDB 100 1.0.1）。

一、定长数据类型验证

1. 创建测试表，字段数据类型分别为char(8000)--定长，binary(8000)-- 定长

SQL> drop table if exists test_to_nchar;
SQL> create table test_to_nchar(name char(8000), addr binary(8000));

Succeed.

SQL>
SQL> desc test_to_nchar

Name                                Null?    Type
----------------------------------- -------- ------------------------------------
NAME                                         CHAR(8000 BYTE)
ADDR                                         BINARY(8000)

SQL>



2. 插入测试数据
SQL> insert into test_to_nchar values ('300000','ABCDEFGH');

1 rows affected.

SQL> commit;

Succeed.

SQL> select * from test_to_nchar;

NAME                                                             ADDR
---------------------------------------------------------------- ----------------------------------------------------------------
300000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           ABCDEFGH

1 rows fetched.

SQL>



3. 查看字段值的字节长度lengthb()
SQL> select lengthb(name),lengthb(addr) from test_to_nchar;

LENGTHB(NAME)        LENGTHB(ADDR)
-------------------- --------------------
8000                 8000

1 rows fetched.

SQL>


结果：to_nchar()函数在转换定长数据类型时，支持最大8000字节

二、变长数据类型验证

1. 创建测试表，字段数据类型为变长varchar，并填充测试数据，字段长度为8000

SQL> drop table if exists test_to_nchar2;
SQL> create table test_to_nchar2 (name varchar(8000));
SQL> insert into test_to_nchar2 values ('1234567890');
SQL> update test_to_nchar2 set name=lpad(name,8000,'ABC');  ---- 字符填充函数LPAD，把字段填充为8000长度
SQL> commit;
SQL> select * from test_to_nchar2;

NAME
----------------------------------------------------------------
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1 rows fetched.

SQL>

2. 查看字段值的字节长度lengthb()

SQL> select lengthb(to_nchar(name)) from test_to_nchar2;

LENGTHB(TO_NCHAR(NAME))
-----------------------
8000

1 rows fetched.

SQL>



结果：to_nchar()函数在转换变长数据类型时，同样支持返回8000字符

-- < END > --