1-bob. Ma`lumotlar bazasining asosiy tushunchalari

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);

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 by 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 by

WHERE a.snum = b.snu AND b.amt = (SELECT MIN (amt) FROM Orders с WHERE c.odate = b.odate)

ORDER BY 3;

Arifmetik operatorlarning ustuvorligi matematikada bo‘lgani kabi bir xil. Agar kerak bo‘lsa, qavslar yordamida operatorlarni qo‘llash tartibi o‘zgartirilishi mumkin - (a + b) * (x / (y-z)). Va yana bir bor takrorlayman, NULL bilan har qanday operatsiya NULL beradi, masalan: 10 + NULL, NULL * 15/3, 100 / NULL - bularning barchasi NULL ga olib keladi. I.e. shunchaki noma'lum qiymatni aytish aniq natijani berolmaydi. So‘rovni tuzishda buni hisobga oling va agar kerak bo‘lsa, NULL qiymatlarni ISNULL, COALEемент funktsiyalari bilan ishlang:

SELECT

ID,Name,

Salary/100*BonusPercent AS Result1, NULL Salary/100*ISNULL(BonusPercent,0) AS Result2, ISNULL Salary/100*COALESCE(BonusPercent,0) AS