使用CASE WHEN进行字符串替换处理

/*

02

03

mysql>

select

*

from

sales;

04

+

-----+------------+--------+--------+--------+------+------------+

05

|
num |

name

|
winter|spring|summer|fall|category|

06

+

-----+------------+--------+--------+--------+------+------------+

07

|
1 |Java |1067 |200 |150 |267 |Holiday|

08

|
2 |C|970 |770 |531 |486 |Profession |

09

|
3 |JavaScript |53 |13 |21 |856 |Literary |

10

|
4 |SQL|782 |357 |168|250 |Profession |

11

|
5 |Oracle |589|795 |367 |284 |Holiday|

12

|
6 |MySQL|953 |582 |336 |489|Literary |

13

|
7 |Cplus|752 |657 |259|478|Literary |

14

|
8|Python |67 |23 |83 |543 |Holiday|

15

|
9|PHP|673 |48|625 |52 |Profession |

16

+

-----+------------+--------+--------+--------+------+------------+

17

9

rows

in

set

(0.01
sec)

18

19

mysql>

SELECT

name

AS

Name

,

20

->

CASE

category

21

->

WHEN

"Holiday"

THEN

"Seasonal"

22

->

WHEN

"Profession"

THEN

"Bi_annual"

23

->

WHEN

"Literary"

THEN

"Random"

END

AS

"Pattern"

24

->

FROM

sales;

25

+

------------+-----------+

26

|

Name

|
Pattern |

27

+

------------+-----------+

28

|
Java |Seasonal|

29

|
C|Bi_annual |

30

|
JavaScript |Random|

31

|
SQL|Bi_annual |

32

|
Oracle |Seasonal|

33

|
MySQL|Random|

34

|
Cplus|Random|

35

|
Python |Seasonal|

36

|
PHP|Bi_annual |

37

+

------------+-----------+

38

9

rows

in

set

(0.00
sec)

39

40

41

*/

42

Drop

table

sales;

43

44

CREATE

TABLE

sales(

45

num
MEDIUMINT

NOT

NULL

AUTO_INCREMENT,

46

name

CHAR

(20),

47

winter

INT

,

48

spring

INT

,

49

summer

INT

,

50

fall

INT

,

51

category

CHAR

(13),

52

primary

key

(num)

53

)type=MyISAM;

54

55

56

insert

into

sales
value(1,

'Java'

,
1067 ,200,150,267,

'Holiday'

);

57

insert

into

sales
value(2,

'C'

,970,770,531,486,

'Profession'

);

58

insert

into

sales
value(3,

'JavaScript'

,53,13,21,856,

'Literary'

);

59

insert

into

sales
value(4,

'SQL'

,782,357,168,250,

'Profession'

);

60

insert

into

sales
value(5,

'Oracle'

,589,795,367,284,

'Holiday'

);

61

insert

into

sales
value(6,

'MySQL'

,953,582,336,489,

'Literary'

);

62

insert

into

sales
value(7,

'Cplus'

,752,657,259,478,

'Literary'

);

63

insert

into

sales
value(8,

'Python'

,67,23,83,543,

'Holiday'

);

64

insert

into

sales
value(9,

'PHP'

,673,48,625,52,

'Profession'

);

65

66

select

*

from

sales;

67

68

69

SELECT

name

AS

Name

,

70

CASE

category

71

WHEN

"Holiday"

THEN

"Seasonal"

72

WHEN

"Profession"

THEN

"Bi_annual"

73

WHEN

"Literary"

THEN

"Random"

END

AS

"Pattern"

74

FROM

sales;

1

SELECT

CASE

WHEN

10*2=30

THEN

'30
correct'

2

WHEN

10*2=40

THEN

'40
correct'

3

ELSE

'Should
be 10*2=20'

4

END

;

1

SELECT

CASE

10*2

2

WHEN

20

THEN

'20
correct'

3

WHEN

30

THEN

'30
correct'

4

WHEN

40

THEN

'40
correct'

5

END

;

01

/*

02

mysql>

SELECT

Name

,RatingID

AS

Rating,

03

->

CASE

RatingID

04

->

WHEN

'R'

THEN

'Under 17 requires an adult.'

05

->

WHEN

'X'

THEN

'No one 17 and under.'

06

->

WHEN

'NR'

THEN

'Use discretion when renting.'

07

->

ELSE

'OK to rentto minors.'

08

->

END

AS

Policy

09

->

FROM

DVDs

10

->

ORDER

BY

Name

;

11

+

-----------+--------+------------------------------+

12

|

Name

|Rating |Policy |

13

+

-----------+--------+------------------------------+

14

|Africa|PG |OK 

to

rent

to

minors.|

15

|Amadeus |PG |OK 

to

rent

to

minors.|

16

|Christmas |NR |Use discretion 

when

renting. |

17

|Doc |G|OK 

to

rent

to

minors.|

18

|Falcon|NR |Use discretion 

when

renting. |

19

|Mash|R|Under 17 requires an adult.|

20

|Show|NR |Use discretion 

when

renting. |

21

|

View

|NR |Use discretion 

when

renting. |

22

+

-----------+--------+------------------------------+

23

8

rows

in

set

(0.01 sec)

24

25

26

*/

27

28

Drop

table

DVDs;

29

30

CREATE

TABLE

DVDs (

31

ID

SMALLINT

NOT

NULL

AUTO_INCREMENT

PRIMARY

KEY

,

32

Name

VARCHAR

(60)

NOT

NULL

,

33

NumDisks TINYINT

NOT

NULL

DEFAULT

1,

34

RatingID

VARCHAR

(4)

NOT

NULL

,

35

StatID

CHAR

(3)

NOT

NULL

36

)

37

ENGINE=INNODB;

38

39

INSERT

INTO

DVDs (

Name

,NumDisks,RatingID,StatID)

40

VALUES

(

'Christmas'

,1,

'NR'

,

's1'

),

41

(

'Doc'

,1,

'G'

,

's2'

),

42

(

'Africa'

,1,

'PG'

,

's1'

),

43

(

'Falcon'

,1,

'NR'

,

's2'

),

44

(

'Amadeus'

,1,

'PG'

,

's2'

),

45

(

'Show'

,2,

'NR'

,

's2'

),

46

(

'View'

,1,

'NR'

,

's1'

),

47

(

'Mash'

,2,

'R'

,

's2'

);

48

49

50

SELECT

Name

,RatingID

AS

Rating,

51

CASE

RatingID

52

WHEN

'R'

THEN

'Under 17 requires an adult.'

53

WHEN

'X'

THEN

'No one 17 and under.'

54

WHEN

'NR'

THEN

'Use discretion when renting.'

55

ELSE

'OK to rentto minors.'

56

END

AS

Policy

57

FROM

DVDs

58

ORDER

BY

Name

;