case when mysql with multiple conditions - mysql

Question

I made the following case when statement in my sql:
SELECT
*,
CASE
WHEN lead_time < 14 THEN 0
WHEN (14 <= lead_time < 21 AND days_passed = 8) THEN 1
WHEN
(21 <= lead_time < 28
AND days_passed = 15)
THEN
1
WHEN
(28 <= lead_time < 42
AND days_passed = 22)
THEN
1
WHEN
(42 <= lead_time < 56
AND days_passed = 36)
THEN
1
WHEN
(56 <= lead_time < 84
AND days_passed = 29)
THEN
1
WHEN
(56 <= lead_time < 84
AND days_passed = 50)
THEN
1
WHEN (lead_time > 84 AND days_passed = 36) THEN 1
WHEN (lead_time > 84 AND days_passed = 57) THEN 1
ELSE 0
END AS send_email
I do not get any error. However, when I check the results I get:
# lead_time, days_passed, send_email
99, 15, 1
99, 22, 1
99, 15, 1
99, 8, 1
99, 8, 1
99, 8, 1
99, 8, 1
85, 29, 1
57, 50, 1
18, 36, 1
99, 22, 1
99, 22, 1
99, 22, 1
99, 22, 1
99, 22, 1
15, 15, 1
15, 15, 1
99, 8, 1
99, 8, 1
99, 8, 1
99, 8, 1
It seems as if the 'and' in the query behaves as an 'or'. Any idea why?.
Thanks,

Answer 1

MySQL doesn't support a syntax:
min <= expr <= max
Such kinds of expressions can be written as:
WHERE expr >= min AND expr <= max
or with using operator BETWEEN (please note that BETWEEN is inclusive):
WHERE expr BETWEEN min AND max
Comparison operators in MySQL: http://dev.mysql.com/doc/refman/5.5/en/comparison-operators.html

Answer 2

The comparison 14 <= lead_time < 21 AND days_passed = 8 is checked in sequence, so in a way you have:
((14 <= lead_time) < 21) AND (days_passed = 8)
Which is always true because 14 <= lead_time equals 1 and thus your comparison is equal to:
( 1 < 21 ) AND days_passed = 8
You should use a between or an and for each comparison.