mysql 去重,跨表更新,跨表删除

一、去重
1.查询出重复的记录

CREATE TABLE push_log_full_2013_10_30_tmp
SELECT * FROM `push_log_full`
WHERE time BETWEEN FROM_DAYS(TO_DAYS(NOW()) - 1) AND FROM_DAYS(TO_DAYS(NOW()))
AND (imsi, andriodid, time) IN (
SELECT imsi, andriodid, time FROM `push_log_full`
WHERE time BETWEEN FROM_DAYS(TO_DAYS(NOW()) - 1) AND FROM_DAYS(TO_DAYS(NOW()))
GROUP BY imsi, andriodid, time
HAVING COUNT(*) > 1)

将重复的记录查出来放到一张临时表里面去。2删除push_log_full表中的重复数据。3将临时表的数据重新导入到push_log_full中。二、跨表更新法一：

UPDATE product p, productPrice pp
SET pp.price = pp.price * 0.8
WHERE p.productId = pp.productId
AND p.dateCreated < '2004-01-01'

法二：

UPDATE product p
INNER JOIN productPrice pp
ON p.productId = pp.productId
SET pp.price = pp.price * 0.8
WHERE p.dateCreated < '2004-01-01'

法三多表更新：

UPDATE product p
INNER JOIN productPrice pp
ON p.productId = pp.productId
SET pp.price = pp.price * 0.8,
p.dateUpdate = CURDATE()
WHERE p.dateCreated < '2004-01-01'

三、跨表删除在Mysql4.0之后，mysql开始支持跨表delete。Mysql可以在一个sql语句中同时删除多表记录，也可以根据多个表之间的关系来删除某一个表中的记录。假定我们有两张表：Product表和ProductPrice表。前者存在Product的基本信息，后者存在Product的价格。第一种跨表删除的方式是不用join，在delete时指定用半角逗号分隔多个表来删除，如下sql语句：

DELETE p.*, pp.*
FROM product p, productPrice pp
WHERE p.productId = pp.productId
AND p.created < '2004-01-01'

第二种跨表删除的方式是使用inner join在join中指定两表之间的关联关系，如下sql语句：

DELETE p.*, pp.*
FROM product p
INNER JOIN productPrice pp
ON p.productId = pp.productId
WHERE p.created < '2004-01-01'

跨表删除也可以使用left join，例如我们要删除所有在ProductPrice表中没有记录的Product表记录。如下sql语句：

DELETE p.*
FROM product p
LEFT JOIN productPrice pp
ON p.productId = pp.productId
WHERE pp.productId is null

单表级联删除

DELETE FROM 4a_org WHERE p_id IN (
SELECT org_id FROM 4a_org_tmp WHERE p_id IN
( SELECT org_id FROM 4a_org_tmp WHERE p_id IN
( SELECT org_id FROM 4a_org_tmp WHERE org_name='江西省') ) ) ; -- 学校DELETE FROM 4a_org WHERE p_id IN (
SELECT org_id FROM 4a_org_tmp WHERE p_id IN (
SELECT org_id FROM 4a_org_tmp WHERE org_name='江西省') ) ; -- 区/县DELETE FROM 4a_org WHERE p_id IN (
SELECT org_id FROM 4a_org_tmp WHERE org_name='江西省' ) ; -- 市DELETE FROM 4a_org WHERE org_name LIKE '%江西省%'; -- 省