Wrong column count for select without row

Issue #13 closed
Former user created an issue

Originally reported on Google Code with ID 13 ``` The column count is set to 0 when a select statement returns no row. This is not the good value. Here is a use case (with empty database): - create table t (c text);

  • step returns false
  • columnCount returns 0 - select * from sqlite_master
  • step returns true (one row for table t)
  • columnCount returns 5 - select * from sqlite_master where name='not_exists'
  • step returns false
  • columnCount returns 0 but 5 was expected

This bug comes from two places: - how SQLiteStatement.step() handle SQLITE_DONE - the use a sqlite3_data_count

The step method sets myColumnCount to COLUMN_COUNT_UNKOWN when sqlite returns SQLITE_ROW and 0 when it returns SQLITE_DONE. But a select without row return SQLITE_DONE. So, line 322 of SQLiteStatement must be changed to:


(and maybe some code refractoring can be done).

The SQLiteStatement.ensureCorrectColumnCount(...) method use sqlite3_data_count. It returns the number of data in the result. If no result (no row) is returned, it returns 0. According to the following comment is sqlite3.c, sqlite3_column_count will returns the right column count:

Set the number of result columns that will be returned by this SQL statement. This is now set at compile time, rather than during execution of the vdbe program so that sqlite3_column_count() can be called on an SQL statement before sqlite3_step().

So, line 1228 must be changed to:

myColumnCount = _SQLiteSwigged.sqlite3_column_count(handle);

I called sqlite3_column_count using reflection and obtained the right value.

A unit test is attached to this issue. ```

Reported by `olivier.monaco@free.fr` on 2010-08-10 08:35:58


Comments (7)

  1. Igor Sereda

    ``` Thanks for an extensive bug report. Will fix soon.

    -- Igor ```

    Reported by `sereda` on 2010-08-10 09:09:38 - Status changed: `Accepted`

  2. Former user Account Deleted

    ``` There's another method to change in SQLiteStatement: the checkColumn method. Now, it's possible to retrieve column information when we don't have a row. So the following code, line 1223, must be removed: if (!myHasRow) throw new SQLiteException(WRAPPER_NO_ROW, null);

    But as a side effect, columnBlob/Double/Int/... must include this code. I've created a checkHasRow() method.

    New patch attached.


    Reported by `olivier.monaco@free.fr` on 2010-08-16 13:09:31


  3. Igor Sereda

    ``` It appears that sqlite3_data_count is safer than sqlite3_column_count, because it always returns the correct value or 0. In some cases sqlite3_column_count may return incorrect value (an example of that later).

    However, for the sake of convenience, I've changed to sqlite3_column_count and documenting the edge cases. ```

    Reported by `sereda` on 2010-08-21 22:15:17

  4. Igor Sereda

    ``` I've fixed the column count, applied your patch (thanks) and did some refactoring. See in revision >= 192.

    The case where sqlite3_column_count would return incorrect result is demonstrated in RegressionIssue13Tests.testUnstableColumnResult - http://code.google.com/p/sqlite4java/source/browse/trunk/test/com/almworks/sqlite4java/RegressionIssue13Tests.java#46

    Will be delivered on Monday. ```

    Reported by `sereda` on 2010-08-21 22:39:51 - Status changed: `Fixed`

  5. Former user Account Deleted

    ``` Thanks.

    I'm not sure the "testUnstableColumnResult" is really a bug. It's more like a design feature. Maybe you can add a comment columnCount about that. ```

    Reported by `olivier.monaco@free.fr` on 2010-08-23 12:15:08

  6. Igor Sereda

    Reported by `sereda` on 2010-08-23 20:10:02 - Status changed: `Delivered` - Labels added: FixVersion-201

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