.Dd January 24, 2024
.Dt SQLITE3_VTAB_NOCHANGE 3
.Os
.Sh NAME
.Nm sqlite3_vtab_nochange
.Nd determine if virtual table column access is for UPDATE
.Sh SYNOPSIS
.In sqlite3.h
.Ft int
.Fo sqlite3_vtab_nochange
.Fa "sqlite3_context*"
.Fc
.Sh DESCRIPTION
If the sqlite3_vtab_nochange(X) routine is called within the xColumn
method of a virtual table, then it might return true if
the column is being fetched as part of an UPDATE operation during which
the column value will not change.
The virtual table implementation can use this hint as permission to
substitute a return value that is less expensive to compute and that
the corresponding xUpdate method understands as a "no-change"
value.
.Pp
If the xColumn method calls sqlite3_vtab_nochange() and finds
that the column is not changed by the UPDATE statement, then the xColumn
method can optionally return without setting a result, without calling
any of the sqlite3_result_xxxxx() interfaces.
In that case, sqlite3_value_nochange(X) will
return true for the same column in the xUpdate method.
.Pp
The sqlite3_vtab_nochange() routine is an optimization.
Virtual table implementations should continue to give a correct answer
even if the sqlite3_vtab_nochange() interface were to always return
false.
In the current implementation, the sqlite3_vtab_nochange() interface
does always returns false for the enhanced UPDATE FROM statement.
.Sh IMPLEMENTATION NOTES
These declarations were extracted from the
interface documentation at line 9828.
.Bd -literal
SQLITE_API int sqlite3_vtab_nochange(sqlite3_context*);
.Ed
.Sh SEE ALSO
.Xr sqlite3_result_blob 3