https://www.cnblogs.com/zeussbook/p/9999052.html
如下：一张订单表多个字段关联用户表：
1.链表查询
SELECT cu.id AS 'id',cu.version AS 'version',cu.cid AS 'cid',cu.uid AS 'uid',cu.shopName AS 'shopName',cu.address AS 'address',
cu.totalPrice AS 'totalPrice',cu.orderType AS 'orderType',
cu.state AS 'state',cu.cCreateTime AS 'cCreateTime',cu.decorate AS 'decorate',cu.area AS 'area',cu.roomArea AS 'roomArea',
cu.machinePrice AS 'machinePrice',cu.caid AS 'caid',
cu.cooperationtypeid AS 'cooperationtypeid',cu.cooperationRebate AS 'cooperationRebate',cu.cooperationPrcie AS 'cooperationPrcie',
cu.machineDiscount AS 'machineDiscount',cu.alreadyPaid AS 'alreadyPaid',cu.updateTime AS 'updateTime',cu.cooperationdeposit AS 'cooperationdeposit',
cu.updateUserid AS 'updateUserid',cu.overseerId AS 'overseerId',cu.decorationQuotation AS 'decorationQuotation',cu.machineDeposit AS 'machineDeposit',
us1.uName AS 'serviceuName',us2.uName AS 'updateName'
FROM `customerorder` AS cu LEFT JOIN `userdetail` AS us1 ON us1.id=cu.uid LEFT JOIN `userdetail` AS us2 ON us2.id=cu.updateUserid
2.子查询
SELECT cu.id AS 'id',cu.version AS 'version',cu.cid AS 'cid',cu.uid AS 'uid',cu.shopName AS 'shopName',cu.address AS 'address',
cu.totalPrice AS 'totalPrice',cu.orderType AS 'orderType',
cu.state AS 'state',cu.cCreateTime AS 'cCreateTime',cu.decorate AS 'decorate',cu.area AS 'area',cu.roomArea AS 'roomArea',
cu.machinePrice AS 'machinePrice',cu.caid AS 'caid',
cu.cooperationtypeid AS 'cooperationtypeid',cu.cooperationRebate AS 'cooperationRebate',cu.cooperationPrcie AS 'cooperationPrcie',
cu.machineDiscount AS 'machineDiscount',cu.alreadyPaid AS 'alreadyPaid',cu.updateTime AS 'updateTime',cu.cooperationdeposit AS 'cooperationdeposit',
cu.updateUserid AS 'updateUserid',cu.overseerId AS 'overseerId',cu.decorationQuotation AS 'decorationQuotation',cu.machineDeposit AS 'machineDeposit',
(SELECT uName FROM `userdetail` WHERE id=cu.uid) AS 'serviceuName',(SELECT uName FROM `userdetail` WHERE id=cu.updateUserid) AS 'updateName'
FROM `customerorder` AS cu
总结：
1，表关联的效率要高于子查询，因为子查询走的是笛卡尔积
2，表关联可能有多条记录，子查询只有一条记录，如果需要唯一的列，最好走子查询