Here are a couple table definitions:
CREATE TABLE `users1` (
`name` varchar(10) default NULL,
`birthday` date default NULL
);
CREATE TABLE `users2` (
`name` varchar(10) default NULL,
`birthday` date default NULL
);
After inserting some data, we get the following row counts:
SELECT COUNT(*) FROM users1;
+----------+
| COUNT(*) |
+----------+
| 15 |
+----------+
SELECT COUNT(*) FROM users2;
+----------+
| COUNT(*) |
+----------+
| 12 |
+----------+
Now, for this query:
SELECT * FROM users1 UNION SELECT * FROM users2;
How many rows will be in the result set? (Choose the best answer)
a) Exactly 27
b) At least 12
c) At least 15
d) Between 1 and 27
e) Zero or more
La commande UNION
l’énigme en français
Trackback by Kamelot Blog — August 25, 2006 @ 7:50 pm