sql 中的 case when(mysql 为例)
发布日期:2021-09-22 22:47:11 浏览次数:16 分类:技术文章

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mysql> SELECT Name, RatingID AS Rating,
-> CASE RatingID
-> WHEN 'R' THEN 'Under 17 requires an adult.'
-> WHEN 'X' THEN 'No one 17 and under.'
-> WHEN 'NR' THEN 'Use discretion when renting.'
-> ELSE 'OK to rent to minors.'
-> END AS Policy
-> FROM DVDs
-> ORDER BY Name;
+-----------+--------+------------------------------+
| Name | Rating | Policy |
+-----------+--------+------------------------------+
| Africa | PG | OK to rent to minors. |
| Amadeus | PG | OK to rent to minors. |
| Christmas | NR | Use discretion when renting. |
| Doc | G | OK to rent to minors. |
| Falcon | NR | Use discretion when renting. |
| Mash | R | Under 17 requires an adult. |
| Show | NR | Use discretion when renting. |
| View | NR | Use discretion when renting. |
+-----------+--------+------------------------------+
8 rows in set (0.01 sec)
*/
Drop table DVDs;
CREATE
TABLE DVDs
(
ID SMALLINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
Name VARCHAR
(
60
)
NOT NULL,
NumDisks TINYINT NOT NULL DEFAULT
1
,
RatingID VARCHAR
(
4
)
NOT NULL,
StatID CHAR
(
3
)
NOT NULL
)
ENGINE=INNODB;
INSERT
INTO DVDs
(
Name, NumDisks, RatingID, StatID
)
VALUES
(
'Ch
ristmas
',
1
,
'NR', 's1'),
(
'Do
c
',
1
,
'G'
,
's2'),
(
'Af
rica
',
1
,
'PG', 's1'),
(
'Fa
lcon
',
1
,
'NR', 's2'),
(
'Am
adeus
',
1
,
'PG', 's2'),
(
'Sh
ow
',
2
,
'NR', 's2'),
(
'Vi
ew
',
1
,
'NR', 's1'),
(
'Ma
sh
',
2
,
'R'
,
's2');
SELECT
Name, RatingID AS Rating,
CASE RatingID
WHEN
'R'
THEN
'Un
der
17
requires an adult.
'
WHEN
'X'
THEN
'No
one
17
and under.
'
WHEN
'NR' T
HEN
'Us
e discretion when renting.
'
ELSE
'OK
to rent to minors.
'
END
AS Policy
FROM
DVDs
ORDER BY Name;

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