oracle, clob type query prompts: 1. The string buffer is too small 2. The data type is inconsistent: it should be -, but the solution of CLOB is obtained

Scenarios where the problem occurs:

First, the database defines the field type in a certain table as CLOB. When this field is used as a query condition and spliced ​​to the end of the where statement, the following prompt will appear:

Or when converting clob type to char type using a function, it prompts that the buffer is too small:

 

Cause of the problem

First of all, the CLOB type cannot be processed and is directly spliced ​​behind the where statement as a condition for equality.

-- 假设id 为 clob类型 当前查询会报错
select t.id from account t where  t.id = '123';

The reason for the error is:

   "123" is a string, t.id is a CLOB type, and cannot be directly connected.

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Secondly, after the CLOB type is converted to string format (varchar2), since varchar2 has an upper limit of 4000 length, it is necessary to limit the length before querying.

Solution:

-- 假设id 为 clob类型 
select t.id from account t where  t.id = '123';

-- 方式一：substr控制长度
select t.id from account t where to_char(substr(t.id,0,4000))t.id = '123';

-- 方式二：dbms_lob.substr控制长度
select t.id from account t where to_char(dbms_lob.substr(t.id,4000,1))t.id = '123';

Of course, if the current clob type variable stores Chinese, since Chinese occupies two characters, the upper limit needs to be divided by 2

-- 假设id 为 clob类型 
select t.id from account t where  t.id = '123';



-- 中文情况 substr 上限除以2
select t.id from account t where to_char(substr(t.id,0,4000))t.id = '123';