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Add comments describing the special sqlite_stat1 handling to sqlite3session.h.

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FossilOrigin-Name: 4431a3256f7436e34b3c33edc1f3e53df7eb3c87daec9bac8d038895d93ca7f2
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dan
2018-01-18 16:53:41 +00:00
parent d1cccf19b5
commit e3ca3831ba
3 changed files with 31 additions and 7 deletions
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24
ext/session/sqlite3session.h
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@ -147,6 +147,30 @@ int sqlite3session_indirect(sqlite3_session *pSession, int bIndirect);
**
** SQLITE_OK is returned if the call completes without error. Or, if an error
** occurs, an SQLite error code (e.g. SQLITE_NOMEM) is returned.
**
** <h3>Special sqlite_stat1 Handling</h3>
**
** The "sqlite_stat1" table is an exception to some of the rules above. In
** SQLite, the schema of sqlite_stat1 is:
** <pre>
** &nbsp; CREATE TABLE sqlite_stat1(tbl,idx,stat)
** </pre>
**
** Even though sqlite_stat1 does not have a PRIMARY KEY, changes are
** recorded for it as if the PRIMARY KEY is (tbl,idx). Additionally, changes
** are recorded for rows for which (idx IS NULL) is true. However, for such
** rows a zero-length blob (SQL value X'') is stored in the changeset or
** patchset instead of a NULL value. This allows such changesets to be
** manipulated by legacy implementations of sqlite3changeset_invert(),
** concat() and similar.
**
** The sqlite3changeset_apply() function automatically converts the
** zero-length blob back to a NULL value when updating the sqlite_stat1
** table. However, if the application calls sqlite3changeset_new(),
** sqlite3changeset_old() or sqlite3changeset_conflict on a changeset
** iterator directly (including on a changeset iterator passed to a
** conflict-handler callback) then the X'' value is returned. The application
** must translate X'' to NULL itself if required.
*/
int sqlite3session_attach(
sqlite3_session *pSession, /* Session object */