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int sqlite3_stmt_explain(sqlite3_stmt *pStmt, int eMode);
The sqlite3_stmt_explain(S,E) interface changes the EXPLAIN setting for prepared statement S. If E is zero, then S becomes a normal prepared statement. If E is 1, then S behaves as if its SQL text began with "EXPLAIN". If E is 2, then S behaves as if its SQL text began with "EXPLAIN QUERY PLAN".
Calling sqlite3_stmt_explain(S,E) might cause S to be reprepared. SQLite tries to avoid a reprepare, but a reprepare might be necessary on the first transition into EXPLAIN or EXPLAIN QUERY PLAN mode.
Because of the potential need to reprepare, a call to sqlite3_stmt_explain(S,E) will fail with SQLITE_ERROR if S cannot be reprepared because it was created using sqlite3_prepare() instead of the newer sqlite3_prepare_v2() or sqlite3_prepare_v3() interfaces and hence has no saved SQL text with which to reprepare.
Changing the explain setting for a prepared statement does not change the original SQL text for the statement. Hence, if the SQL text originally began with EXPLAIN or EXPLAIN QUERY PLAN, but sqlite3_stmt_explain(S,0) is called to convert the statement into an ordinary statement, the EXPLAIN or EXPLAIN QUERY PLAN keywords will still appear in the sqlite3_sql(S) output, even though the statement now acts like a normal SQL statement.
This routine returns SQLITE_OK if the explain mode is successfully changed, or an error code if the explain mode could not be changed. The explain mode cannot be changed while a statement is active. Hence, it is good practice to call sqlite3_reset(S) immediately prior to calling sqlite3_stmt_explain(S,E).