數(shù)據(jù)庫基礎(chǔ)教程6第六章sql中的約束和觸發(fā)程序(參考版)
2024-10-11 16:40本頁面
【正文】 48 包含 Trigger的 SQL Create Assertion RichPrss After Insert On Studio。 END Execute update_dept 123,212,’cs’,’98001’ 42 SQL3中的觸發(fā)程序 Trigger ? 約束是基于數(shù)據(jù)變化的 ? Trigger則是基于對(duì)表的操作（動(dòng)作）的 ? 當(dāng)指定的表上發(fā)生特定的操作，系統(tǒng)便激活 Trigger程序 ? 大部分 DBMS產(chǎn)品均支持 Trigger ? 觸發(fā)器類型 ? Insert / Update / Delete / Column Update ? Rowlevel / StatementLevel ? Before / After 43 Trigger—— 類型 ? 觸發(fā)器類型 ? Insert / Update / Delete / Column Update ? Rowlevel / StatementLevel ? Before / After / Instead Of ? Old Value/ New Value 44 Trigger—— 示例 Create Trigger NetWorthTrigger After Update Of Worth On MovieExec referencing Old As OldTuple,New As NewTuple When( ) Update MovieExec Set Worth = Where cert = For Each Row 名稱 激活的時(shí)機(jī) 事件 新值 /修改后的值 舊值 /修改前的值 執(zhí)行程序的條件 每修改一個(gè)元組便激活 45 Trigger—— 示例 Create Trigger NetWorthTrigger After Update Of Worth On MovieExec referencing Old As OldTuple,New As NewTuple When( ) Update MovieExec Set Worth = Where cert = For Each Row 名稱 激活的時(shí)機(jī) 事件 新值 /修改后的值 舊值 /修改前的值 執(zhí)行程序的條件 每修改一個(gè)元組便激活 46 Trigger—— 示例 for each row Create Trigger NetWorthTrigger After Update Of Worth On MovieExec referencing Old As OldTuple,New As NewTuple When( ) Update MovieExec Set Worth = Where cert = For Each Row 47 Trigger—— 示例 for each statement Create Trigger AvgNetWorthTrigger Instead Of Update Of Worth On MovieExec referencing Old_Table As OldStuff,New_Table As NewStuff When(500000=Select Avg(Worth) From (MovieExec Except OldStuff)) Union NewStuff) Delete From MovieExec Where (name,address,c
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