SQLite

Consider the following test case:

CREATE TABLE t0(c0 UNIQUE AS(0), c1, c2);
INSERT INTO t0(c1) VALUES(0);
UPDATE t0 SET c1 = 0, c2 = 0 WHERE(c0) >= 0; -- sqlite3.c:72305: sqlite3BtreeInsert: Assertion `pCur->curFlags & BTCF_ValidNKey' failed.

When compiling with -DSQLITE_DEBUG, the UPDATE triggers an assertion error.

Other ways of provoking this problem:

CREATE TABLE t1(a TEXT, b INTEGER PRIMARY KEY UNIQUE); 
INSERT INTO t1 VALUES(1,2);
UPDATE t1 SET a = quote(b) WHERE b>=2;

The redundant UNIQUE on the PRIMARY KEY is required for the problem to occur.

Also:

CREATE TABLE t1(a INTEGER PRIMARY KEY,b);
CREATE INDEX t1x1 ON t1(a+25);
INSERT INTO t1(a,b) VALUES(75,33);
UPDATE t1 SET b=1 WHERE a+25=100;