. .
, - .
, .
U, , , , .
, . W, .
, .
, , .
, (=).
. .
, .
.
∆ 6 : <x1,y1;x2,y2;x3,y3>, (x1,y1), (x2,y2), (x3,y3) .
n .
α= <a1,a2,,an>, . ak k k α.
, , , , .
.. α =<x1,,xm>
β = <y1,,yn>
m = n
xk = yk
.
, , .
1, 2, , n. () , 1*2**n, , <a1,a2,,an> k, akϵAk, 1≤k≤n.
, .
. .
- .
, , b, ϵ .
R *.
.
R
≤
.
R , : , .
Qb a ~b
R
.
.
R , .
R 2 , , .
|
|
.
.
.
.
.
<, ≤.
, .
, , =>x≤y.. . .
x≤y
.
- . :
, :
1. =
2. (\ )
. , .
< , ≤ (, ) .
.
R 1*2 , :
1. (,) ϵ R (,) ϵ R, = z( )
2. .
n- ( n)
n- , , , , 2 .
- , , , , . : , 40 80 . 50 . 40 50 . , -, , , .
( , . ), .
1. {, , }
2. {, , }
3. {, , }
2 :
1. 1-3
2. 4-6
1-2 R,
R1 **Q, Q .
([x,y,z) ϵR1 ó n.
R1 R1 .
() | () | Q |
4-6, R2
|
|
R2 **
(z,y,x) ϵR2
C () | () | () |
R2 ,
Ω = **
3*3*3 = 27
, ,
Ω - .
R2 .
, R2 .
, 3 (3-), 3 .
.
R .
R Ṝ, (,) :
1. (,) ϵ R
2. z1,z2,,znϵA, (, z1)(z1,z2),,(zn,y) ϵ
= {, ; , ; , }
.
R ( ⅻ)
Ṝ :
Ṝ , . , , , .. , .
.
1. . .
2. .
3. .
( )
( )
()
.
1970. , .
. , 3 :
1.
2.
3.
1. , . , , n- .
2. , . , .
3. 2 , .
, .
: ,
, .
3 :
1.
2.
3.
01.03.12
: SQL
SELECT
Select , . . (ALL , ). , *.
|
|
Select
SELECT [ALL|DISTINCT] ( | *)
FROM ( )
[WHERE ( ) ]
[GROUP BY ( )]
[HAVING ( )]
[ORDER BY ( , )]
ALL ,
DISTINCT , ,
* ,
FROM FROM ().
WHERE .
GROUP BY .
HAVING , .
ORDER BY .
WHERE :
1. (<,>,<=,<>)
2. between A and B
3. IN
4. LIKE NOT LIKE
5. IS NULL
: R1, R2, R3
.1: Select *
From r1,r2;
! .
.2: ( . .)
Select r1.a, r2.b
From r1,r2;
( r1, b r2. .
.3:( )
Select distinct
From r3
.4:
Select
From r1
Where = Ĕ and = 5;
.5: ,
Select ,
From r2, r3
Where r2 = r3 ;
where r2, r3, . (). r3, , .
. , ( 2)
Select distinct r1.
From r1 a, r1 b
Where a.=b. and
a. <> b.
a.<=2 and b. <=2;
(a,b) r1, b r1.
sql
-CHARACTER (n) CHAR(n) n
-NUMERIC [(n,m)] . n , n
-DECIMAL [(n,m)]
-DEC[(n,m)]
-INTEGER INT
-SMALLINT , .
-FLOA [(n)] , , n , .
-REAL FLOAT.
|
|
-DOUBE PRECISION REAL
-VARCHAR (n) n.
-NCHAR(N) , (n)
-NCHAR VARYING
-DATE
-TIMESTAMP()-
-INTERVAL
. .
Count | |
Sum | |
Avg | |
Min | |
Max |
.
Select r1., count(*)
From r1
Group by r.;
Count(*) | |
/ |
.
Select count(*)
From r1
Where >2;
.
Select r1., count(distinct r.)
From r1
Where r1.<>0
group by r1.;
.
Select r2., r1., count(*) avg()
From r1,r2
Where r1. = r2. and
R1.>2 and r1.<>0
Group by r1., r1.;
.
Select r2.
From r1,r2
Where r1. = r2. and
R1.=2
Group by r2., r1.
Having count(*)>1;
22.03.2012
:
1.
2. .
3.
4.
5..
6. 3
7.
: select _ from T1,T2,,Tn () .
! , , .
. .
: select _ from MyTab T1, My Tab T2;
(select _ from T1, T2,,Tn;)
(union)
, .
: 1 union 2;
. , union all.
: . . , :
Select , from
Union
Select , , from ;
, . , union distinct.
union ,
1.
2. . , () char varchar ,
(intersect)
, , .
: 1 intersect 2;
.
! union intersect corresponding. , .
: 1 2. .
Select *from 1
Intersect
Select *from 2;
(except)
: 1 except 2;
.
|
|
:
.
Select* from
Except*from ;
(Join)
(natural join)
2 :
(ID_, , ID_);
(ID_, , )
:
select *from , ;
, , (. ID_=. ID_). , .
. : select .*, ., .
From ,
Where .ID_=.ID_;
natural join
Select .*, ., .
From Natural join ;
! Access natural join , inner join ( ), on (), .
(joinon)
. , , , on( where), , .
:
2
(ID_, -, ID_);
(ID_, , )
: select *from JOIN
On (.ID_)=.ID_)
And (.>50);
(joinusing)
. , , .
: select* from ,
Where (.=.) and (.-=.-);
! access joinusing , inner joinon. access : select* from inner join
On (.=. ) and (.-=.=);
. join inner join. , , , .
, .
(left outer join)
, , , .
:
(ID_,,);
(ID_, -);
! outer , left join.
Right outer join ,
Full join. .
:
- ;
- ,
, , , , :
Select*
From full join
On (.ID_=.ID_)
Full join
On (.ID_=.ID_)
, . , . , , , .
SQL, .
Commit . .
Rollback . , , .
Savepoint . , .
[i]
201
5.04
12.04
26.04
r1, r2, r3
r1
r2
r3
access
[i]