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## SQLite C Interface

## Concatenate Two Changeset Objects

>     int sqlite3changeset_concat(
>       int nA,                         /* Number of bytes in buffer pA */
>       void *pA,                       /* Pointer to buffer containing changeset A */
>       int nB,                         /* Number of bytes in buffer pB */
>       void *pB,                       /* Pointer to buffer containing changeset B */
>       int *pnOut,                     /* OUT: Number of bytes in output changeset */
>       void **ppOut                    /* OUT: Buffer containing output changeset */
>     );

This function is used to concatenate two changesets, A and B, into a single changeset. The result is a changeset equivalent to applying changeset A followed by changeset B.

Rows are identified by the values in their PRIMARY KEY columns. A change in changeset A is considered to apply to the same row as a change in changeset B if the two rows have the same primary key.

Changes to rows that appear only in changeset A or B are copied into the output changeset. Or, if both changeset A and B contain a change that applies to a single row, the output depends on the type of each change, as follows:

Change A | Change B | Output Change
--- | --- | ---
INSERT | INSERT | Change A is copied into the output changeset. Change B is discarded. This case does not occur if changeset B is recorded immediately after changeset A.
INSERT | UPDATE | An INSERT change is copied into the output changeset. The values in the INSERT change are as if the row was inserted by change A and then updated according to change B.
INSERT | DELETE | No change at all is copied into the output changeset.
UPDATE | INSERT | Change A is copied into the output changeset. Change B is discarded. This case does not occur if changeset B is recorded immediately after changeset A.
UPDATE | UPDATE | A single UPDATE is copied into the output changeset. The accompanying values are as if the row was updated once by change A and then again by change B.
UPDATE | DELETE | A single DELETE is copied into the output changeset.
DELETE | INSERT | If one or more of the column values in the row inserted by change B differ from those in the row deleted by change A, an UPDATE change is added to the output changeset. Otherwise, if the inserted row is exactly the same as the deleted row, no change is added to the output changeset.
DELETE | UPDATE | Change A is copied into the output changeset. Change B is discarded. This case does not occur if changeset B is recorded immediately after changeset A.
DELETE | DELETE | Change A is copied into the output changeset. Change B is discarded. This case does not occur if changeset B is recorded immediately after changeset A.

If the two changesets contain changes to the same table, then the number of columns and the position of the primary key columns for the table must be the same in each changeset. If this is not the case, attempting to concatenate the two changesets together fails and this function returns SQLITE_SCHEMA. If either of the two input changesets appear to be corrupt, and the corruption is detected, SQLITE_CORRUPT is returned. Or, if an out-of-memory condition occurs during processing, this function returns SQLITE_NOMEM.

If none of the above errors occur, SQLITE_OK is returned and *ppOut set to point to a buffer containing the output changeset. It is the responsibility of the caller to eventually call sqlite3_free() on *ppOut to release memory allocated for the buffer. *pnOut is set to the number of bytes in the output changeset. If an error does occur, both *ppOut and *pnOut are set to zero before returning.

See also lists of Objects, Constants, and Functions.