select count(1)、 count(字段名) 、count(*) 的区别 如果一张表tmp 有10个字段 select * from tmp; 和 select 字段1,字段2,字段3...字段10 from tmp;
就是把 ( select field1 as 订单号, field2 as 客户名称, field24 as 订单金额, field13 as 商品名称, '销售订单' as 类型 from u_table218 )这个子查询得到的结果作为一张临时表，然后从这个表中查询数据，而这个表的名字就叫做tmp，这种作为临时表处理的子查询叫做内嵌视图。
SELECT COUNT(id) as sp_counter FROM () sp_tmp_table_pager1 执行错误: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') sp_tmp_table_pager1' at line 1 ...
select uin, max(tmp_count) as max_continuation_date_cnt from ( select uin, count(ftime - rk) as tmp_count from _牛客网_牛客在手,offer不愁
declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1 open cur_rows fetch cur_rows into @id,@max while @@fetch_status=0 begin select @max = @max -1 set rowcount @max delete from 表名 where 主字段 = @id fetch cur...
我们将count和distinct两个操作分开: SELECT COUNT(*) as cnt FROM (SELECT DISTINCT id, a, b FROM test_distinct) as tmp; 1. 嗯?结果是正确的,那就说明count(distinct expr)生成的查询计划可能和我们想象的不一样,并不是先去重再统计,使用explain分析一下两条语句的查询计划,如下所示: ...
count(distinct order_no) as order_num from tmp.big_traffic_data_three_new group by dep_city,arr_city 对这条sql的理解,有几条航线结果肯定就是几条数据,如果一个order_no在同一个航线中出现了两次,那肯定会被去重的,但如果她是在多条航线中各出现了一次那肯定会被保存多次的。
select into语句是创建并填充数据，into后面是新表表名 数据来源是from后面的表
{ FIRST | LAST } ]} [, ...] ] [ LIMIT { [offset,] count | ALL } ] [ OFFSET start [ ROW | ROWS ] ] [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ] [ {FOR { UPDATE | NO KEY UPDATE | SHARE | KEY SHARE } [ OF table_name [, ...] ] [ NOWAIT |...
一个参数的方法方式 1 DECLARE cnt INT DEFAULT 0; select count(*) into cnt from test_tbl; select cnt; 方式 2 set...@cnt = (select count(*) from test_tbl); select @cnt; 方式 3...