1、inner join
left join right join on (两表结合的）条件 where 各个表的条件
一个多表相连的例子
"UPDATE doc_project_schedule SET item_insideSpent = ( SELECT sum(paid.item_paid_fee) FROM t_document INNER JOIN doc_purchase_item_paid paid ON t_document.MAPPINGID = paid.id WHERE t_document.PARENT IN ( SELECT t_document.ID
FROM t_document INNER JOIN doc_purchase_item_contains items ON t_document.MAPPINGID = items.ID WHERE items.item_belong_purchaseplan_map_id IN ( SELECT item_sys_id FROM doc_purchase_plan WHERE item_project_belong_id = '"+projectId+"' )) AND paid.item_state
= '审核通过' AND paid.item_has_paid = '是' ) WHERE item_project_doc_id = '"+projectId+"'"
FROM t_document INNER JOIN doc_purchase_item_contains items ON t_document.MAPPINGID = items.ID WHERE items.item_belong_purchaseplan_map_id IN ( SELECT item_sys_id FROM doc_purchase_plan WHERE item_project_belong_id = '"+projectId+"' )) AND paid.item_state
= '审核通过' AND paid.item_has_paid = '是' ) WHERE item_project_doc_id = '"+projectId+"'"
2 、update
1)update 表名 set 值 where 条件
2) 带条件的update 语句
UPDATE t_user INNER JOIN t_user_no set LOGINNO = (SELECT t_user_no.FINANCENO
from t_user_no where t_user.LOGINNO = t_user_no.OFFICENO) WHERE t_user.LOGINNO = t_user_no.OFFICENO
from t_user_no where t_user.LOGINNO = t_user_no.OFFICENO) WHERE t_user.LOGINNO = t_user_no.OFFICENO
3)变量给所有列加一个序号字段
3、 union
UNION 指令的目的是将两个 SQL 语句的结果合并起来。从这个角度来看， UNION 跟 JOIN 有些许类似，因为这两个指令都可以由多个表格中撷取资料。 UNION 的一个限制是两个 SQL 语句所产生的栏位需要是同样的资料种类。另外，当我们用
UNION这个指令时，我们只会看到不同的资料值 (类似 SELECT DISTINCT)。 union只是将两个结果联结起来一起显示，并不是联结两个表……