我应该绑定哪种数据类型作为查询参数，以与Oracle ODBC中的NUMBER（15）列一起使用？

Question

I have just been bitten by issue described in SO question Binding int64 (SQL_BIGINT) as query parameter causes error during execution in Oracle 10g ODBC .

I'm porting a C/C++ application using ODBC 2 from SQL Server to Oracle. For numeric fields exceeding NUMBER(9) it uses __int64 datatype which is bound to queries as SQL_C_SBIGINT. Apparently such binding is not supported by Oracle ODBC. I must now do an application wide conversion to another method. Since I don't have much time---it's an unexpected issue---I would rather use proved solution, not trial and error.

What datatype should be used to bind as eg NUMBER(15) in Oracle? Is there documented recommended solution? What are you using? Any suggestions?

I'm especially interested in solutions that do not require any additional conversions. I can easily provide and consume numbers in form of __int64 or char* (normal non-exponential form without thousands separator or decimal point). Any other format requires additional conversion on my part.

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What I have tried so far:

SQL_C_CHAR

Looks like it's going to work for me. I was worried about variability of number format. But in my use case it doesn't seem to matter. Apparently only fraction point character changes with system language settings.

And I don't see why I should use explicit cast (eg TO_NUMERIC) in SQL INSERT or UPDATE command. Everything works fine when I bind parameter with SQL_C_CHAR as C type and SQL_NUMERIC (with proper precision and scale) as SQL type. I couldn't reproduce any data corruption effect.

SQL_NUMERIC_STRUCT

I've noticed SQL_NUMERIC_STRUCT added with ODBC 3.0 and decided to give it a try. I am disappointed.

In my situation it is enough, as the application doesn't really use fractional numbers. But as a general solution... Simply, I don't get it. I mean, I finally understood how it is supposed to be used. What I don't get is: why anyone would introduce new struct of this kind and then make it work this way .

SQL_NUMERIC_STRUCT has all the needed fields to represent any NUMERIC (or NUMBER, or DECIMAL) value with it's precision and scale. Only they are not used.

When reading, ODBC sets precision of the number (based on precision of the column; except that Oracle returns bigger precision, eg 20 for NUMBER(15)). But if your column has fractional part (scale > 0) it is by default truncated. To read number with proper scale you need to set precision and scale yourself with SQLSetDescField call before fetching data.

When writing, Oracle thankfully respects scale contained in SQL_NUMERIC_STRUCT. But ODBC spec doesn't mandate it and MS SQL Server ignores this value. So, back to SQLSetDescField again.

See HOWTO: Retrieving Numeric Data with SQL_NUMERIC_STRUCT and INF: How to Use SQL_C_NUMERIC Data Type with Numeric Data for more information.

Why ODBC doesn't fully use its own SQL_NUMERIC_STRUCT? I don't know. It looks like it works but I think it's just too much work.

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I guess I'll use SQL_C_CHAR.

Answer 1

My personal preference is to make the bind variables character strings (VARCHAR2), and let Oracle do the conversion from character to it's own internal storage format. It's easy enough (in C) to get data values represented as null terminated strings, in an acceptable format.

So, instead of writing SQL like this:

SET MY_NUMBER_COL = :b1
  , MY_DATE_COL = :b2

I write the SQL like this:

SET MY_NUMBER_COL = TO_NUMBER( :b1 )
  , MY_DATE_COL   = TO_DATE( :b2 , 'YYYY-MM-DD HH24:MI:SS')

and supply character strings as the bind variables.

There are a couple of advantages to this approach.

One is that works around the issues and bugs one encounters with binding other data types.

Another advantage is that bind values are easier to decipher on an Oracle event 10046 trace.

Also, an EXPLAIN PLAN (I believe) expects all bind variables to be VARCHAR2, so that means the statement being explained is slightly different than the actual statement being executed (due to the implicit data conversions when the datatypes of the bind arguments in the actual statement are not VARCHAR2.)

And (less important) when I'm testing of the statement in TOAD, it's easier just to be able to type in strings in the input boxes, and not have to muck with changing the datatype in a dropdown list box.

I also let the buitin TO_NUMBER and TO_DATE functions validate the data. (In earlier versions of Oracle at least, I encountered issues with binding a DATE value directly, and it bypassed (at least some of) the validity checking, and allowed invalid date values to be stored in the database.

This is just a personal preference, based on past experience. I use this same approach with Perl DBD.

I wonder what Tom Kyte (asktom.oracle.com) has to say about this topic?