最近看了尚硅谷的zookeeper教程,在集群环境搭建中, 有这么一个脚本zk.sh用来一键启动和查询
#!/bin/bash
case $1 in
"start"){
for i in zknode2 zknode3 zknode4
doecho ---------- zookeeper $i 启动 ------------
ssh $i "/opt/modu…
比如在Northwind数据库中有一个查询为SELECT c.CustomerId,CompanyName FROM Customers cWHERE EXISTS(SELECT OrderID FROM Orders o WHERE o.CustomerIDc.CustomerID)这里面的EXISTS是如何运作呢?子查询返回的是OrderId字段,可是外面的查询要找的是Cus…