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Don Burleson Blog 







ORA-12704 character set mismatch

Oracle Database Tips by Donald BurlesonMay 5, 2016

Question: What causes the ORA-12704 error?  I am doing a SQL UNION ALL query:

ORA-12704 character set mismatch

What is the fix for the ORA-12704 error?

Answer:  The oerr utility shows this for the ORA-12704 error:

ORA-12704 character set mismatch

Cause: One of the following:

  •  The string operands (other than an NLSPARAMS argument) to an operator or built-in function do not have the same character set.

  • An NLSPARAMS operand is not in the database character set.

  • String data with character set other than the database character set is passed to a built-in function not expecting it.

  • The second argument to CHR() or CSCONVERT() is not CHAR_CS or NCHAR_CS.

  • A string expression in the VALUES clause of an INSERT statement, or the SET clause of an UPDATE statement, does not have the same character set as the column into which the value would be inserted.

  • A value provided in a DEFAULT clause when creating a table does not have the same character set as declared for the column.

  • An argument to a PL/SQL function does not conform to the character set requirements of the corresponding parameter.

Action: Strings declared with NCHAR or NCHAR VARYING do not interoperate with strings declared with CHAR or VARCHAR2. Use TRANSLATE() function to explicitly convert one to the other.

As we see, the ORA-12704 error can have many fixes and solutions.  This little demonstration shows the ORA-12704 error:

SQL> create table tbl1(x varchar2(10));

Table created.

SQL> create table tbl2(x nvarchar2(10));

Table created.

SQL> select * from tbl1 union all select * from tbl2;
select * from tbl1 union all select * from tbl2
ERROR at line 1:

ORA-12704: character set mismatch

here we see how a CAST operator can fix an ORA-12704 error:

SQL> select test from mytest union select '' from mytest;
select test from mytest union select '' from mytest
ERROR at line 1:
ORA-12704: character set mismatch

SQL> select test from mytest union select cast('' as nvarchar2(100)) from mytest;


Here wee see how a UNION all character set mismatch was solved with a "translate" command:

select a.product from my_product a
union all
select 'Overall' from my_product b;

Aafter I translate the column 'Overall' into nchar_cs, the problem is fixed,

select a.product from my_product a
union all
select translate ('Overall' using nchar_cs) product from my_product b;

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