MySQL Bugs: #56717: SQLDescribeCol and SQLColAttribute cannot be called before SQLExecute

Bug #56717	SQLDescribeCol and SQLColAttribute cannot be called before SQLExecute
Submitted:	10 Sep 2010 16:20	Modified:	16 Sep 2010 16:46
Reporter:	Lawrenty Novitsky	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Connector / ODBC	Severity:	S3 (Non-critical)
Version:	5.1.7	OS:	Any
Assigned to:	Lawrenty Novitsky	CPU Architecture:	Any

Description:
SQLDescribeCol and SQLColAttribute cannot be called before SQLExecute if query is parametrized and not all parameters are bound.
MSDN says that "For performance reasons, an application should not call SQLColAttribute/SQLDescribeCol  before executing a statement."
But that doesn't mean that that shouldn't be possible to do.

How to repeat:
In the testcase for the Bug#56677 substitute call of SQLNumResultCols to call of SQLColAttribute/SQLDescribeCol and make the query parametrized.

Suggested fix:
do "dummy" parameter bind for unbound parameters

didn't push as i'm not sure we really need that

the patch

Attachment: bug56717.diff (text/x-diff), 3.90 KiB.

Lawrin,

The patch looks ok, but I would like to extend the test case by adding checking the number of result cols (SQLNumResultCols()) after SQLDescribeCol() to fit the real life example. Also, verifying data after reading looks logical:

.......

  is_str(colname, "tt_varchar", 11);
  is_num(collen, 128);

  /* Just to make sure that SQLNumResultCols still works fine */
  ok_stmt(hstmt, SQLNumResultCols(hstmt, &colCount));

  is_num(colCount, 1);

  ok_stmt(hstmt, SQLBindParameter(hstmt, 1, SQL_PARAM_INPUT, SQL_C_LONG, SQL_INTEGER, 0, 0, &nData, 0, NULL));
  ok_stmt(hstmt, SQLBindCol(hstmt, 1, SQL_C_CHAR, szData, sizeof(szData),
    NULL));

  ok_stmt(hstmt, SQLExecute(hstmt));

  ok_stmt(hstmt, SQLFetch(hstmt));
  is_str(szData, "string 3", 8);

  ok_stmt(hstmt, SQLFetch(hstmt));

  is_str(szData, "string 4", 8);

  /* Closing statement and preparing query again to make sure that query isn't "dummy-executed"*/
  ok_stmt(hstmt, SQLFreeStmt(hstmt, SQL_CLOSE));

....

Patch with requested modifications and ChangeLog entries has been pushed as rev#929 If stars align properly it will be released in 5.1.8

final variant of the patch

Attachment: bug56717v2.diff (text/x-diff), 4.48 KiB.

An entry has been added to the 5.1.8 changelog:

SQLDescribeCol and SQLColAttribute could not be called before SQLExecute, if the query was parameterized and not all parameters were bound.

Note, MSDN states that “For performance reasons, an application should not call SQLColAttribute/SQLDescribeCol before executing a statement.” However, it should still be possible to do so if performance reasons are not paramount.