Yesterday’s Pop Quiz seemed quite popular, I got some personal responses and a couple of funny comments.
So here’s another one:
The table t is defined thusly on a MySQL server with no sql modes set:
CREATE TABLE t ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT );
You now do…
INSERT INTO t (id) VALUES (NULL); SELECT * FROM t WHERE id IS NULL
What will be the result of the SELECT?
The table t is defined thus:
CREATE TABLE t ( id INT NOT NULL, data CHAR(30) DEFAULT NULL, UNIQUE (id, data) );
You now do…
INSERT INTO t VALUES (1, NULL);
Which causes one row to be inserted into the table. Keeping in
mind that the UNIQUE index spans across both columns, what would
happen if you were to repeat the INSERT command?
Spanish translation by Marcos Besteiro
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