sql 优化

SELECT
g.*, p.product_id AS product_id,
p.specs AS product_specs,
b. NAME AS brand_name,
t. NAME AS type_name,
c. NAME AS cat_name

FROM
product p

LEFT JOIN  goods g ON p.goods_id = g.goods_id

LEFT JOIN  goods_cat c ON g.cat_id = c.cat_id

LEFT JOIN  brand b ON g.brand_id = b.brand_id

AND b.disabled = 0

LEFT JOIN es_goods_type t ON g.type_id = t.type_id

WHERE
g.market_enable = 1

AND g.disabled = 0

AND g.sn LIKE 'SAB2107839%'

ORDER BY

goods_id DESC

1，查询条件sn加索引   create index idx_product  on     product (sn);



2,like 'sn%'    不能出现 like '%sn%' , 否则sn加的索引就不起作用



3，最好不要出现 g.*，需要什么字段，查询出来



4,做更新语句的时候，最好保持sql的原子性，不要查询出来再加减，拼接。考虑到并发情况下会有脏数据出现，

建议写成 ：

直接加减：

 update cart set num=num+? where  product_id=? （整型，例如购物车的数据等）

直接拼接：

String sql="update product p set p.name=concat(p.name,'"+spec+"') where  p.goods_id>=400108    and p.goods_id<=403855 and  p.sn='"+sn+"'";




5，sql替换

UPDATe goods SET `intro`=REPLACE(`intro`,'pl201604/beyotime','pl201605/beyotime')  WHERE  goods_id >=673951 AND goods_id <= 674885 




sql拼接

update es_product  set sn=concat(sn,'-',specs) where  goods_id >=680138  and  goods_id<=691447