Mundarija kirish mavzu

SQL muhitida tranzaksiyalani boshqarish. 
SQL tilida tranzaksiyalami maxsus
operatorlat yordamida
boshqarish imkoniyati mavjud. Shulardan biri tranzaksiya parametrlarini
o‟matish operatori bo'lib, uniyozilish formati quyidgicha:
::=
SET TRANSACTION transaction mode> [ { transaction
mode> }... ]
transaction mode> ::=

|
| «diagnostics size>

«isolation level> ::=
ISOLATION LEVEL «level of isolation>
::=
READ UNCOMMITTED | READ COMMITTED i REPEATABLE
READ | SERIALIZAB1 1
transaction access mode>

---

90
READ ONLY | READ WRITE

diagnostics size> ::=
DIAGNOSTICS SIZE
::=
Bu yerda:
 Agar himoya darajalari ko'rsatilmasa, himoya darajasi
SERIALIZABLE deb tushumniladi.
 Agar ruxsat tartibi READWRITE kalit so'zi bilan belgilansa, unda
himoyalanish darajasi READUNCOMMITTED bo'lmasligi kerak.
 Agar
ruzsat
tartibi
va
himoyalanish
darajasi
READUNCOMMITTED deb ko'rsatilsa, unda beriladigan ruxsat
tartibi READONLY deb tushuniladi, aks hollarda ruxsat tartibi
READWRITE bo'ladi.
Ko'pchilik hollarda tranzaksiyalaming bajarilish jarayonida MB
jadvallari stmkturasi buzilishining oldini olish uchun tranzaksiyalarga
faqat o'qish tartibini o'rnatish mumkin. Buning uchun quyidagi operator
ishlatiladi:
SET TRANSACTION READ ONLY;
Bu operator tranzaksiya jarayoni boshlanishidan oldin ko'rsatiladi.
Masalan, EXEC SQL SET TRANSACTION READ ONLY;
Buyurtmalarni qabul qilgan sotuvchini aniqlamoqchmiz. Bu ikki
so‟rovni bir- biridan farq qilishi uchun matn kiritish yo'li bilan
tashkillashtirisimiz mumkin:
SELECT a.snum, sname, onum, ‟Highest on‟, odate FROM Salespeople
a.
Orders b WHERE a.snum = b.snum AND b.amt = (SELECT MAX
(amt) FROM Orders с WHERE c.odate = b,odate)
UNION
SELECT a.snum, sname, onum, ‟Lowest on‟, odate FROM Salespeople
a, Orders b WHERE a.snum b.snum AND b.amt = (SEi FCT MIN
(amt)FROM Orders с WHERE c.odate ; b.odate);
10 Peel 30
High o 10/05/
10 Peel
30
Low o 10/05/
10 Peel
30
High o 10/06/
10 Serre 30 High o 10/03/
10 Serre 30 Low o 10/04/
10 Serre 30 Low o 10/06/

---

91
10 Axel 30 High o 10/04/

Shu paytgacha UNION kalit so‟zi yordamida birlashtirilgan so'rov
natijalari qanday tartibda matnga chiqarilishi to'g‟risida gapirmadik.
Birlashtirilgan
natijalarni ORDER
BY
kalit so'zi yordamida
tartiblashtirish mumkin. Yoqoridagi misolni tartub raqamlariga nisbatan
tartiblashni ko'rib o'tamiz.
SELECT a.snum, sname, onum, ‟Highest on‟, odate FROM Salespeople
a. Orders b WHERE a.snum = b.snum AND b.amt = (SELECT MAX
(amt) FROM Orders с WHERE c.odate = b.odate)
UNION
SELECT a.snum, sname, onum. ‟Lowest on‟, odate F ROM Salespeople
a. Orders b WHERE a.snum = b.snu AND b.amt = (SELECT MIN (amt)
FROM Orders с WHERE c.odate = b.odate) ORDER BY 3; Natija
quyidagicha:
1007 Rifkin
3001
Lowest on
10/03/199
1002 Serres
3005
Highest on
10/03/199
1002 Serres
3007
lowest on
10/04/199
1001 Peel
3008
Highest on
10/05/199
1001 Peel
3008
Lowest on
10/05/199
1003 Axelrod
3009
Highest on
10/04/199
1002 Serres
3010
Lowest on
10/06/199
1001 Peel
3011
Highest on
10/06/199