mysql 查

獲取表格有多少行
技巧：

select count(*) from table_name;

取出cat_id=4和cat_id=11的列
使用or select * from goods where cat_id=4 or cat_id=11;
不使用or select * good (4,11); 

取出價格>=100 且

select * from goods where shop_price >= 100 and shop_price <= 500;
select * from goods where shop_price between 100 and 500;

取出價格=500

select * from goods where shop_price <=100 and shop_price >= 500;
select * from goods where shop_price not between 100 and 500;

in是散點的集合，between and

select * from goods where cat_id!=3 and cat_id!=11;
select * from goods where cat_id not in(3,11);

in是散點的集合，between and是
3也不是11的欄位

select goods_id,(market_price-shop_price) as chajia ,goods_name from goods ;

算出比市價優惠的數值

select goods_id,(market_price-shop_price) as chajia ,goods_name from goods where (market_price - shop_price) > 200;

查找本地價格比市價便宜200以上的

select goods_id,(market_price-shop_price) as chajia ,goods_name from goods where chajia > 200;(错误的)

的作用


）

疑點注意：where是對真實表中的資料發揮作用，having可以對where結果進行過濾

select goods_id,(market_price-shop_price) as chajia ,goods_name from goods having chajia>200;

作用相同

update mian set num = floor(num/10)*10 where num between 20 and 39;

把mian表中的num列中[20,29] 20 [30,39]改為30

select goods_id ,goods_name,substring(goods_name,4) from goods where goods_name like '诺基亚%';

like模糊查詢

截取諾基亞後面的內容

select goods_id ,goods_name,concat('htc',substring(goods_name,4)) from goods where goods_name like '诺基亚%';

查找有諾基亞開頭的更換為htc（沒有更改真實表）

update goods 
set goods_name = concat('htc',substring(goods_name,4))
where goods_name like '诺基亚%' and cat_id=4;

查找有諾基亞開頭的更換為htc（沒有更改真實表）

。 htc（更改真實表格內容）

rrreee

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