【MongoDB】mongoimport and mongoexport of data (一),mongodbmongoimportIn the software development, we usually are faced with a common question of exporting or importing data from database. So in this blog we will together study the mongoddb export and
mysql子查詢慢的問題,mysql子問題 當你在用explain工具查看sql語句的執行計畫時,若select_type 欄位中出現“DEPENDENT SUBQUERY”時,你要注意了,你已經掉入了mysql子查詢慢的“坑"。。。下面我們來看一個具體的例子有這樣一條查詢語句:SELECT gid,COUNT(id) as count FROM shop_goods g1 WHERE status =0 and gid IN (SELECT
TNS-01251: Cannot set trace/log directory under ADR,tns-01251adr11204 RAC 環境報錯 TNS-01251: Cannot set trace/log directory under ADR LSNRCTL> set current_listener listener Current Listener is listenerLSNRCTL> set current_listener listener
資料庫的檢索語句,資料庫檢索語句1、SELECT 基本用法 1.1簡單的資料檢索1.1.1檢索出需要的列 只要執行“SELECT * FROM 名”即可。SELECT * FROM T_Employee 。SELECT * FROM T_Employee語句會把資料庫的所有列的資訊從資料庫中讀出來,緩衝到記憶體中。檢索出所有的列的 SQL 陳述式為“SELECT * FROM
set,setup SQL> set echo on-----------------設定運行命令是是否顯示語句 SQL> set feedback on----------------設定顯示“已選擇XX行” SQL> set colsep | -----------------設定列與列之間的分割符號 SQL> set pagesize 10----------------設定每一頁的行數 SQL> SET SERVEROUTPUT ON-
OR導致笛卡爾積,or笛卡爾最近監控資料庫,發現下面語句跑得非常慢,原來執行計畫走了導致笛卡爾積,來看下面語句:SQL> explain plan for 2 SELECT COUNT(*) 3 FROM "GD_FS"."TZZ_SJ_DEV_DISC_79073" "A2", 4 "GD_FS"."TZZ_SJ_DEVELOP_MONTH"
MySQL觸發器 trigger之for each row,mysqltriggerfor each row 每行受影響,觸發器都執行,叫行級觸發器。oracle 觸發器中分行級觸發器和語句級觸發器,可不寫for each row,無論影響多少行都只執行一次。mysql不支援語句觸發器,所以必須寫for each row;實際操作驗證:#觸發器test5:DELIMITER $$CREATE TRIGGER test5AFTERUPDATEON goodsFOR EACH ROWBEGIN