1. CCT1343, Week 2 Single-Table SQL Yuri Takhteyev University of Toronto
January 10, 2011
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2. Connect to the Server ssh kenobio7@yoda.ischool.utoronto.ca
If you are on Windows and do not have git-bash, install from:

3. Important Keys command completion earlier commands quit
“Ctrl+C” is usually
represented as “^C”
image source:

4. MySQL Prompt mysql> do not confuse with the bash prompt!
Hint: type “exit” or ^C to exit.
What do we enter at the mysql prompt?

5. mysql> show databases;
Available Databases
mysql> show databases;
| Database |
| information_schema |
| child_care |
| diveshop |
| kenobio |
| menagerie |
| starwars |
6 rows in set (0.00 sec)

6. mysql> use menagerie;
Selecting a Database
mysql> use menagerie;
Database changed

7. mysql> show tables;
Listing Tables
mysql> show tables;
| Tables_in_menagerie |
| event |
| owner |
| pet |
| species |
4 rows in set (0.00 sec)

8. mysql> describe pet;
Describing a Table
mysql> describe pet;
| Field | Type | Null | Key | Default | Extra |
| name | varchar(20) | YES | | NULL | |
| owner | varchar(20) | YES | | NULL | |
| species | varchar(20) | YES | | NULL | |
| sex | char(1) | YES | | NULL | |
| birth | date | YES | | NULL | |
| death | date | YES | | NULL | |
| weight | float | YES | | NULL | |
7 rows in set (0.00 sec)

9. Relation “name” “species” “birth” “owner” “sex”
(Fluffy, Harold, cat, f, )
(Buffy, Harold, dog, f, )
(Chirpy, Gwen, bird, f, )
“name”
“species”
“birth”
“owner”
“sex”

10. A Table name Fluffy Bluffy Chirpy owner Harold Gwen species cat dog
bird
sex f
birth

11. Order Doesn't Matter (in most cases) birth 1993-02-04 1989-05-13
owner
Harold
Gwen
name
Fluffy
Bluffy
Chirpy
sex f
species
cat
dog
bird

12. Projection name Fluffy Bluffy Chirpy owner Harold Gwen species cat dog
bird
sex f
birth

13. Projection πname, species, sex(R) name Fluffy Bluffy Chirpy species
cat
dog
bird
sex f
πname, species, sex(R)

14. (“Restriction” in Harrington)
Selection
(“Restriction” in Harrington)
name
Fluffy
Bluffy
Chirpy
owner
Harold
Gwen
species
cat
dog
bird
sex f
birth

15. (“Restriction” in Harrington)
Selection
(“Restriction” in Harrington)
name
Fluffy
Bluffy
owner
Harold
species
cat
dog
sex f
birth
σFluffy, Buffy(R)
owner=”Harold”
name = “Fluffy”
or name = “Bluffy”

16. Columns vs Rows Projection: choosing columns (fields) by name
Selection:
choosing rows with a condition

17. selection followed by projection
Basic SELECT 3. 1. 2.
select
«list of fields»
from «souce table»
where «conditions»;
selection followed by projection

18. For Instance: select name, weight from pet where owner="Harold";
From table pet,
select rows satisfying the condition
owner=”Harold”,
then return fields name and weight.

19. mysql> select name from pet -> where owner="Harold";
Selection in SQL
mysql> select name from pet
-> where owner="Harold";
| name | weight |
| Fluffy | |
| Buffy | |
2 rows in set (0.00 sec)

20. select * from «table» where «condition»;
Skipping Projection
select *
from «table»
where «condition»;
For instance:
select *
from pet
where owner="Harold";

21. +--------+--------+---------+------+------------+-------+--------+
| name | owner | species | sex | birth | death | weight |
| Fluffy | Harold | cat | f | | NULL | |
| Buffy | Harold | dog | f | | NULL | |
2 rows in set (0.01 sec)

22. select «fields» from «table» where «condition1» and «condition2»;
Complex Conditions
select «fields» from «table»
where «condition1» and «condition2»;
For instance:
select name, weight
from pet
where owner="Harold"
and species="dog";

23.
| name | weight |
| Buffy | |
1 row in set (0.00 sec)

24. select «fields» from «table» where «condition1» or «condition2»;
Or We Can Use “OR"
select «fields» from «table»
where «condition1» or «condition2»;
For instance:
select name, owner, species
from pet
where owner="Harold"
or species="dog";

25. +--------+--------+---------+
| name | owner | species |
| Fluffy | Harold | cat |
| Buffy | Harold | dog |
| Fang | Benny | dog |
| Bowser | Diane | dog |
4 rows in set (0.00 sec)

26. select «fields» from «table» where not «condition»;
And Why Not “NOT”?
select «fields» from «table»
where not «condition»;
For instance:
select name, owner from pet
where not owner="Harold";

27. +----------+-------+
| name | owner |
| Claws | Gwen |
| Fang | Benny |
| Bowser | Diane |
| Chirpy | Gwen |
| Whistler | Gwen |
| Slim | Benny |
| Puffball | Diane |
7 rows in set (0.00 sec)

28. «condition1» and not («condition2» or «condition3»)
Combinations
«condition1» and
not («condition2» or «condition3»)
For instance:
select name from pet
where species="dog" and
not (owner="Harold" or owner="Gwen");

29.
| name |
| Fang |
| Bowser |
2 rows in set (0.00 sec)

30. «field» = «value» «value» = «value» «field» = «field»
Fields and Values
«field» = «value»
«value» = «value»
«field» = «field»
For instance:
select name, owner
from pet
where name=owner;

31.
| name | owner |
| Margie | Margie |
1 row in set (0.00 sec)

32. An Odd Case "Harold"="Harold" What will we get back?
select name, owner
from pet
where "Harold"="Harold";

33. +----------+--------+
| name | owner |
| Fluffy | Harold |
| Claws | Gwen |
| Buffy | Harold |
| Fang | Benny |
| Bowser | Diane |
| Chirpy | Gwen |
| Whistler | Gwen |
| Slim | Benny |
| Puffball | Diane |
| Margie | Margie |
10 rows in set (0.00 sec)

34. Another Odd Case "Harold"="Gwen" What will we get back?
select name, owner
from pet
where "Harold"="Gwen";

35. Empty set (0.00 sec)

36. «value» = «function»(«value»)
Functions
«value» = «function»(«value»)
For instance:
select name, owner
from pet
where upper(name)="buffy";

37.
| name | owner |
| Buffy | Harold |
1 row in set (0.00 sec)

38. where «value»=«value»;
Tests: Equality
where «value»=«value»;
For instance:
select name from pet
where owner="Harold";

39. where «value»!=«value»;
Tests: Inequality
where «value»!=«value»;
For instance:
select name, owner from pet
where owner!="Harold";

40. +----------+-------+
| name | owner |
| Claws | Gwen |
| Fang | Benny |
| Bowser | Diane |
| Chirpy | Gwen |
| Whistler | Gwen |
| Slim | Benny |
| Puffball | Diane |
7 rows in set (0.00 sec)

41. where «field» like «pattern»;
Tests: LIKE
where «field» like «pattern»;
For instance:
select name from pet
where name like "%uff%";

42.
| name |
| Fluffy |
| Buffy |
| Puffball |
3 rows in set (0.00 sec)

43. More: >, <, <=, >=
where «value»<«value»;
For instance:
select name, birth from pet
where birth<" ";

44. +--------+------------+
| name | birth |
| Bowser | |
1 row in set (0.00 sec)

45. «expression» > «expression»
Expressions
«expression» > «expression»
For instance:
select name from pet
where weight>birth_weight*50;

46.
| name |
| Fluffy |
| Fang |
| Bowser |
3 rows in set (0.01 sec)

47. Combinations For instance: select name from pet
where species="dog" and
not (owner="Harold" or owner="Gwen")
and weight>birth_weight*50;

48. Combinations For instance: select name from pet where species="dog"
and
not (owner="Harold"
or owner="Harold")
and weight>birth_weight*50;

49.
| name |
| Fang |
| Bowser |
2 rows in set (0.00 sec)

50. Complex Projection For instance: select upper(name), weight/1000
from pet
where species="dog";

51. Complex Projection For instance: select upper(name),
round(weight/1000,3)
from pet
where species="dog";

52. +-------------+----------------------+
| upper(name) | round(weight/1000,3) |
| BUFFY | |
| FANG | |
| BOWSER | |
3 rows in set (0.00 sec)

53. mysql> describe pet;
The 6th Column
mysql> describe pet;
| Field | Type | Null | Key | Default | Extra |
| name | varchar(20) | YES | | NULL | |
| owner | varchar(20) | YES | | NULL | |
| species | varchar(20) | YES | | NULL | |
| sex | char(1) | YES | | NULL | |
| birth | date | YES | | NULL | |
| death | date | YES | | NULL | |
| weight | float | YES | | NULL | |
7 rows in set (0.00 sec)

54. mysql> select name, death > from pet;
What’s in it?
mysql> select name, death
> from pet;
| name | death |
| Fluffy | NULL |
| Claws | NULL |
| Buffy | NULL |
| Fang | NULL |
| Bowser | |
| Chirpy | NULL |
| Whistler | NULL |
| Slim | NULL |
| Puffball | NULL |
9 rows in set (0.00 sec)
NULL = no value provided (unknown, does not apply, etc.)

55. IS NULL where «field» is null; For instance:
select name, death from pet
where death is null;

56. +----------+-------+
| name | death |
| Fluffy | NULL |
| Claws | NULL |
| Buffy | NULL |
| Fang | NULL |
| Chirpy | NULL |
| Whistler | NULL |
| Slim | NULL |
| Puffball | NULL |
8 rows in set (0.00 sec)

57. “IS NULL” vs “= NULL” death="NULL" death=NULL
true if the value of death is equal to
the four-letter sting “NULL”
death=NULL
always evaluates to NULL (the
condition fails)
death is NULL
evaluates to TRUE is death is null
and to FALSE if death is not null

58. where «field» is not null;
For instance:
select name, death from pet
where death is not null;

59. +--------+------------+
| name | death |
| Bowser | |
1 row in set (0.00 sec)

60. Null with And and Or Null and True → Null Null and False → False
Null or True → True
Null or False → Null

61. Duplicates
For instance:
select species
from pet
where owner="Gwen";

62.
| species |
| cat |
| bird |
3 rows in set (0.00 sec)

63. select distinct «fields» ...
Removing Duplicates
select distinct «fields» ...
For instance:
select distinct species
from pet where owner="Gwen";

64. vs +---------+ | species | | cat | | bird | 2 rows in set (0.00 sec)

65. More SELECT 4. 1. 2. 3. 5. select «list of fields» from «souce table»
where «conditions»
order by «field»
limit «field»;

66. select ... from ... where ... order by «expression»;
Sorting the Results
select ... from ... where ... order by «expression»;
For instance:
select name, birth from pet order by birth;

67. +----------+------------+
| name | birth |
| Bowser | |
| Buffy | |
| Fang | |
| Fluffy | |
| Claws | |
| Slim | |
| Whistler | |
| Chirpy | |
| Puffball | |
9 rows in set (0.01 sec)

68. select ... from ... where ... order by «expression» desc;
Descending Order
select ... from ... where ... order by «expression» desc;
For instance:
select name, birth from pet order by birth desc;

69. LIMIT select ... from ... limit «N»; For instance:
select name, birth from pet order by birth limit 5;

70. +--------+------------+
| name | birth |
| Bowser | |
| Buffy | |
| Fang | |
| Fluffy | |
| Claws | |
5 rows in set (0.00 sec)

71. getting back less then one row per matched record
Aggregation
getting back less then one row per matched record

72. select upper(name) from pet where birth<"1994-12-31";
A “Normal” Function
select upper(name) from pet
where birth<" ";

73.
| upper(name) |
| FLUFFY |
| CLAWS |
| BUFFY |
| FANG |
| BOWSER |
5 rows in set (0.00 sec)

74. select count(<fields>) from ...;
Aggregating: COUNT
select count(<fields>) from ...;
For instance:
select count(name) from pet
where birth<" ";

75.
| count(name) |
| |
1 row in set (0.00 sec)

76. Counting Distinct select count(distinct owner) from pet
where birth<" ";

77. +-----------------------+
| count(distinct owner) |
| |
1 row in set (0.00 sec)

78. Summation
select sum(weight) from pet
where species="cat";

79.
| sum(weight) |
| |
1 row in set (0.00 sec)

80. More Aggregation AVG, MIN, MAX For instance:
select min(weight) from pet;

81. +-------------------+
| min(weight) |
| |
1 row in set (0.00 sec)

82. Grouping ... group by <fields>; For instance:
select species, sum(weight) from pet group by species;

83. +---------+-------------------+
| species | sum(weight) |
| bird | |
| cat | |
| dog | |
| hamster | |
| snake | |
5 rows in set (0.02 sec)

84. HAVING select species, sum(weight) from pet group by species
having sum(weight)<1;
Similar to “where” conditions, but uses aggregate functions (or the grouping fields).

85. +---------+-------------------+
| species | sum(weight) |
| bird | |
| hamster | |
| snake | |
3 rows in set (0.00 sec)

86. HAVING group by species... ...having sum(weight)>10
...having avg(weight)>10
...having weight<1
...having species="dog"
...having name="Buffy"
...having count(name)>1
...having count(species)>1 + -

87. HAVING select species, sum(weight) from pet group by species
having sum(weight)<1;
Similar to “where” conditions, but uses aggregate functions (or the grouping fields).

88. The Order 6. 1. 2. 3. 4. 5. 7. select «list of fields»
from «souce table»
where «conditions»
group by «field»
having «conditions»
order by «field»
limit «field»;

89. The Order 6. 1. 2. 3. 4. 5. 7. weight>1 species count(name)>1
sum(weight)
select
weight
from pet
where
group by
having
order by
limit 1;

90.
| birth |
| |
1 row in set (0.00 sec)

91. Questions?

92. INSERT add a new record UPDATE modify existing record
Data Modification
INSERT
add a new record
UPDATE
modify existing record

93. UPDATE
update pet
set weigh=100
where name="Buffy";

94. INSERT
insert into pet
values ("Margie", "Margie", "pony", "f", " ", NULL, 72);
here order matters!

95. Assignment 1 1. Will be posted later today 2. To be done individually*
3. Provide explanations for queries
4. Build queries in steps
5. Plan for trial and error