GEIC693PWR321U
觸發(fā)器可通過(guò)數(shù)據(jù)庫(kù)中的相關(guān)表實(shí)現(xiàn)級(jí)聯(lián)更改,不過(guò),通過(guò)級(jí)聯(lián)引用完整性約束可以更有效地執(zhí)行這些更改。觸發(fā)器可以強(qiáng)制用比CHECK約束定義的約束更為復(fù)雜的約束。與 CHECK 約束不同,觸發(fā)器可以引用其它表中的列。例如,觸發(fā)器可以使用另一個(gè)表中的 SELECT 比較插入或更新的數(shù)據(jù),以及執(zhí)行其它操作,如修改數(shù)據(jù)或顯示用戶定義錯(cuò)誤信息。觸發(fā)器也可以評(píng)估數(shù)據(jù)修改前后的表狀態(tài),并根據(jù)其差異采取對(duì)策。一個(gè)表中的多個(gè)同類觸發(fā)器(INSERT、UPDATE 或 DELETE)允許采取多個(gè)不同的對(duì)策以響應(yīng)同一個(gè)修改語(yǔ)句。
觸發(fā)器和約束編輯
約束和觸發(fā)器在特殊情況下各有優(yōu)勢(shì)。觸發(fā)器的主要好處在于它們可以包含使用 Transact-SQL 代碼的復(fù)雜處理邏輯。因此,觸發(fā)器可以支持約束的所有功能;但它在所給出的功能上并不總是好的方法。實(shí)體完整性總應(yīng)在低級(jí)別上通過(guò)索引進(jìn)行強(qiáng)制,這些索引或是 PRIMARY KEY 和 UNIQUE 約束的一部分,或是在約束之外獨(dú)立創(chuàng)建的。假設(shè)功能可以滿足應(yīng)用程序的功能需求,域完整性應(yīng)通過(guò) CHECK 約束進(jìn)行強(qiáng)制,而引用完整性(RI) 則應(yīng)通過(guò) FOREIGN KEY 約束進(jìn)行強(qiáng)制。在約束所支持的功能無(wú)法滿足應(yīng)用程序的功能要求時(shí),觸發(fā)器就極為有用。
例如:除非 REFERENCES 子句定義了級(jí)聯(lián)引用操作,否則 FOREIGN KEY 約束只能以與另一列中的值完全匹配的值來(lái)驗(yàn)證列值。
Kollmorgen 00-00907-002 Type U9M4T Servodisc DC Motor
Kollmorgen - Servo Disc DC Motor - Model# UP-00946-040 Type U9M4H-9FA41 Untested
Kollmorgen - Servo Disc DC Motor - Model# 0000946014 Type U9M4H-9FA4T Untested
Kollmorgen - Servo Disc DC Motor - Model# 0000946014 Type U9M4H-9FA4T Untested
Kollmorgen - Servo Disc DC Motor - Model #00D12A07100-2 Type #U12DT-A
Zia Tech ZT 488 GPIB Analyzer Ziatech
ZIATECH BIOS V3.11 FOR ZT 8808/09 Location 5D
ZIATECH BIOS V3.11 FOR ZT 8816/17 ODD / EVEN Location
ZIATECH Ketris 2000 3U CompactPCI chassis, cards, ps, hdd. Tested & working
ZIATECH ZT 192 Parallel IO Board - ZT 14CT72 w/ Warranty
ZIATECH ZT 200 18 SLOT CARD CAGE USED
Ziatech ZT 2225 Interface Adapter PCB-2225-0
ZIATECH ZT 5531 w/ ZT 96073 CPU CompactPCI Board
Ziatech ZT 8809A SBC Single Board Computer PCB Card 15-0023-01 15-0023-02 Used
ZIATECH ZT 8845 I/O BOARD ZT8845
ZIATECH ZT 8845 I/O BOARD ZT8845 Working Pull
Ziatech ZT 8902 Rev:A .1 CPU Board & ZVID1 BUS VGA Adapter & Cabling
Ziatech ZT 8907 single board computer with graphics card intel 486
Ziatech ZT 8953 Rev: 0.2 ALCTNCD 85mb Hard Drive IDE Interface Board ZT 8953-80
Ziatech ZT 8954A-D1 Circuit Board ZT 8954
ZIATECH ZT 8954-D1 Rev. 0.3 Floppy Disk Controller ZT 8954 Interface Board NOS
Ziatech ZT 8995 D2 Rev A.2 Ethernet Interface ++ NICE ++
Ziatech ZT/2 IEEE 488 Interface for PS/2 Computers, GPIB/HPIB Board
Ziatech ZT8088 REV C.2 Memory CPU Circuit Board Card
ZIATECH ZT8830 CONTROL PROCESS BOARD * USED *
ZIATECH ZT8840 REV B NEW OLD STOCK
Ziatech ZT8850 STD Bus Disk Interface board
Ziatech ZT8851 FD1036A STD Bus 3.5" Floppy Disk Drive + Board
Ziatech ZT88CT75 Circuit Board Revision
Ziatech ZT88CT75 Circuit Board Revision A New with Manual
ZIATECH ZT8901 REV A 1.1 BOARD ZT 8901
Ziatech ZT8902 SBC MEMORY CPU PCB ASSY BIOS 4.41 ZT 8902
Ziatech ZT-8902 SBC Single Board Computer PCB Card 486 ZT-8902-S1320 AS-IS
Ziatech ZT8910(16)-2 386SX 16Mhz STD Bus 32 CPU Board
Ziatech ZT8932 Serial control PCB Rev 1 ZT 8932
Ziatech ZT8952 IDE Interface ASSY Rev 0.2