SQL基础学习

1.普通查询

select * from [TName]

查询表【TName】表的所有数据和字段

select Name from [TName]

查询当前表指定的字段

select distinct Tel from [YP_Store] 
查询某列不相同的数据distinct

select distinct Tel ,Name from [YP_Store] where CreatonTime >= '2021-04-12 00:00:00'

查询时间的比较

select distinct Tel ,Id from [YP_Store] order by Id

排序Id

select distinct Tel ,Id from [YP_Store] order by Id desc
相反顺序倒序desc、正序Asc

2.Top获取前几个数据

SELECT TOP 2 * FROM Persons

3. like 查找相似的字段数据

SQL 通配符

4. in 和where使用表示在某个字段中筛选想要的字段值

select * from [YP_Store] where Name in('Name')

5.between 查询条件介于什么范围之间

select * from [YP_Store] where Name between '' and '111'

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6.linq 连表查询

    var query1 = from x in context.YP_Store where x.Id == 2 select new { x.Name, x.Id };
                    var query2 = from x in  context.YP_Account select new { x.Id,x.Name,x.StoreId};
                    var query3 = from t1 in query1 join t2 in query2 on t1.Id equals t2.StoreId select new { SN=t1.Name,AN=t2.Name};
                    var data = query3.ToList();

                    var query4 = from t1 in from x in context.YP_Store where x.Id == 2 select new { x.Name, x.Id } join t2 in from x in context.YP_Account select new { x.Id, x.Name, x.StoreId } on t1.Id equals t2.StoreId select new { SN = t1.Name, AN = t2.Name };
                    var data2 = query3.ToList();

data等于data2；

7.linq 分组查询

                    var query1 = (from x in _IMembersMoneyPayItemRecordService.GetAll()
                                  where x.CreatonTime >= BeginTime && x.IsDeleted == false
                                  group x by x.PayType into g
                                  select new { ActualChange = g.Sum(y => y.ActualChange), PayType = g.Key }).ToList();

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8.sql跨表更新字段

UPDATE `v3城市对应经纬度`, city_info
SET city_info.latitude = `v3城市对应经纬度`.latitude,city_info.longitude = `v3城市对应经纬度`.longitude
WHERE `v3城市对应经纬度`.CtiyId = city_info.cityCode

9.sql更新某个表的字段

-- 更新某个字段
UPDATE device_item 
SET supplier="linglu"
WHERE supplier IS NULL