SQL语法整理

SELECT

1	SELECT attribute-expression-list

2	FROM relation-list

3	[ WHERE condition ];

attribute-expression-list:

[relation-name.]attribute
[relation-name.]attribute [arithmatic computation] AS another name

i.e., E.Salary - 40000 AS SalaryDiff

CASE WHEN ...THEN ...
ELSE ...END

i.e., CASE WHEN E.Salary < 40000 THEN 0

ELSE E.Salary - 40000 END
relation-list:

list of table names
seperate by comma

condition:

arithmetic operation +, -, *, /
comparisions =, <>, <, <=, >. >=
logical connectives AND, OR, NOT
attribute IN (Q)
attribute NOT IN (Q)
attribute op SOME (Q)
attribute op ALL (Q)
EXISTS (Q)
NOT EXISTS (Q)
IS [NOT] NULL

NULL

AND Table

AND	TRUE	FALSE	NULL
TRUE	TRUE	FALSE	NULL
FALSE	FALSE	FALSE	FALSE
NULL	NULL	FALSE	NULL

OR Table

OR	TRUE	FALSE	NULL
TRUE	TRUE	TRUE	TRUE
FALSE	TRUE	FALSE	NULL
NULL	TRUE	NULL	NULL

NOT Table

NOT	TRUE	FALSE	NULL
	FALSE	TRUE	NULL

UNION INTERSECT EXCEPT

(Q1 and Q2 must have same attribute-list)

Q1 UNION Q2 => Together all the tuples in Q1 and Q2

Q1 INTERSECT Q2 => Only tuples in both Q1 and Q2

Q1 EXCEPT Q2 => Tuples only in Q1 but not in Q2

ALL关键字: 允许重复

UNION ALL will include twice of duplicate tuples

INTERSECT ALL will include all possible pairs of match tuples, duplication possible

EXCEPT ALL will include all "not in Q2" tuples, duplication possible

[INNER]/OUTER JOIN

Inner join把两个表连接在一起, 返回两个表中相匹配的记录, 是2和3的交集
Left outer join, 左侧表所有的记录都返回, 右侧匹配的记录返回, 没有匹配的返回Null
Right outer join, 与Left outer join相反, 右侧的记录返回, 左侧返回匹配的记录, 没有匹配返回Null
Full outer join, 2和3的并集
Cross join, 两个表的笛卡儿积, 返回所有可能的值, 不允许有连接条件

ORDER BY

1	SELECT ...

2

...

3	ORDER BY attribute [ DESC / ASC ], attribute [ DESC / ASC ], ......

Note: 如果没有指定Order, return的数据可能是任意顺序

GROUP BY, H***ING, Aggregate expressions

{count, sum, avg, min, max} => Aggregate expressions

Order: Group => Having => Aggregate

count(*): number of tuples
count(E): number of tupple for which E is non-NULL
count(distinct E): number of distinct non-NULL E values
sum(E)
sum(distinct E)
avg(E)
avg(distinct E)
min(E)
max(E)

Note: 没有被group by指定的attribute不能出现在SELECT的attr-list中, 除非是aggregate

INSERT INTO

1	INSERT INTO relation- name

2	[(attribute-list )]

3	VALUE (value-list );

DELETE

1	DELETE FROM relation- name

2	[ WHERE condition ];

UPDATE

1	UPDATE relation- name

2	SET attribute-assignment-list

3	[ WHERE condition ];

attribute-assignment-list:

pairs of assignment
seperate by comma
i.e., WorkDept = 'E01', Address = 'Waterloo'

CREATE TABLE

1	CREATE TABLE relation- name (

2	attribute- name attribute-type [constraints-list],

3

...

4

)

attribute-type: http://www.w3school.com.cn/sql/sql_datatypes.asp
constraints-list: (Constraints的格式在各种数据库中都不太一样, 就不列举了)

NOT NULL
PRIMARY KEY
UNIQUE
FOREIGN KEY
Column or Tuple CHECK

CREATE VIEW

1	CREATE VIEW view - name AS (

2	SELECT ...

3

)

从View SELECT的方法和table一样

CREATE TRIGGER

1	CREATE TRIGGER trigger - name

2	AFTER UPDATE OF attribute-list ON relation- name

3	REFERENCING OLD as instance- name (o) NEW as instance- name (n)

4	FOR EACH ROW

5

...

不同database语法不一