From 63847496f14c813a5d80efd5b7de0f1294ffe1e3 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sat, 13 Apr 2024 16:07:11 +0200 Subject: Adding upstream version 3.45.1. Signed-off-by: Daniel Baumann --- www/c3ref/vtab_nochange.html | 151 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 151 insertions(+) create mode 100644 www/c3ref/vtab_nochange.html (limited to 'www/c3ref/vtab_nochange.html') diff --git a/www/c3ref/vtab_nochange.html b/www/c3ref/vtab_nochange.html new file mode 100644 index 0000000..0f42503 --- /dev/null +++ b/www/c3ref/vtab_nochange.html @@ -0,0 +1,151 @@ + + + + + +Determine If Virtual Table Column Access Is For UPDATE + + + +
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+Small. Fast. Reliable.
Choose any three. +
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SQLite C Interface

 +

Determine If Virtual Table Column Access Is For UPDATE

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+int sqlite3_vtab_nochange(sqlite3_context*);
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+

+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.

+ +

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.

+ +

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. +

See also lists of + Objects, + Constants, and + Functions.

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