收到错误ORA-01722：编号无效，正在运行查询

Question

I am running below query and getting this error:

ORA-01722: invalid number
01722. 00000 -  "invalid number"
*Cause:    The specified number was invalid.
*Action:   Specify a valid number.

select DECODE(upper(db_param_DATA_TYPE),'VARCHAR2',data_length,upper(db_param_DATA_TYPE),'DATE',data_length,
            upper(db_param_DATA_TYPE),'NUMBER',decode(
                nvl(
                    data_scale,
                    0
                ),
                0,
                nvl(
                    data_precision,
                    0
                ),
                data_precision
                 || '.'
                 || data_scale
            ))  
from db_param a 
   join all_tab_columns b on a.db_param_COL_NAME=b.column_name; 

Answer 1

Your query tries to compare a numeric value( data_length ) with string type values 'VARCHAR2' that yields to produce ORA-01722 .

I've just considered the following query which's using all_tab_columns dictionary view as data source :

select decode(upper(DATA_TYPE),
          'VARCHAR2',
          to_char(data_length),
   -- if "to_char(data_length)" replaced with "data_length", you get ORA-01722
          upper(DATA_TYPE),
          'DATE',
          data_length,
          upper(DATA_TYPE),
          'NUMBER',
          decode(nvl(data_scale, 0),
                 0,
                 nvl(data_precision, 0),
                 data_precision || '.' || data_scale))
  from all_tab_columns b
 where b.column_name = upper('&i_column_name'); -- a column in any table of the db. 

Answer 2

The issue lies in the way you have used decode - it does not work in the way I think you think it works.

You have said:

DECODE(upper(db_param_data_type),
       'VARCHAR2',
       data_length,
       upper(db_param_data_type),
       'DATE',
       data_length,
       upper(db_param_data_type),
       'NUMBER',
       DECODE(NVL(data_scale, 0), 0, NVL(data_precision, 0), data_precision || '.' || data_scale))

but what I think you mean is:

DECODE(upper(db_param_data_type),
       'VARCHAR2',
       data_length,
       'DATE',
       data_length,
       'NUMBER',
       DECODE(NVL(data_scale, 0), 0, NVL(data_precision, 0), data_precision || '.' || data_scale))

ie you did not need to repeat the upper(db_param_data_type) throughout the decode.

Decode works by taking a value and then comparing it and outputting the various responses, like so:

decode (<value being checked>
        <if val1>
        <then output result1>
        <if val2>
        <then output result2>
        ...
        <else output result_else>)

so you only ever define the value being checked right at the start.