-- 下面的left join由于主表是t2其中的customer_id比t3多,因此会导致t2的某些行total_cnt_after为null值 -- -- 对观察日之前有过拜访记录的客户打上标签 -- select t2.customer_id -- ,t3.total_cnt_after -- ,case when t3.total_cnt_after>0 then 1 else 0 end as is_active -- from t2 --...
SELECT mdate, team1, SUM(CASE WHEN teamid = team1 THEN 1 ELSE 0 END) AS score1, team2, SUM(CASE WHEN teamid = team2 THEN 1 ELSE 0 END) AS score2 FROM game LEFT OUTER JOIN goal ON(game.id = goal.matchid) GROUP BY mdate, id, team1, team2; 注释: 这道题的大概意思就是...
外连接(Outer Join)是一种 SQL 查询中常用的连接操作,它与内连接(Inner Join)的不同之处在于:外连接不仅返回两个表中匹配的记录,还会返回某一表中没有匹配的记录,并将其与另一个表的空值(NULL)一起展示。外连接主要有三种类型:左外连接(Left Outer Join)、右外连接(Right Outer Join)和全外连接(Full Oute...
'U盘类型'=caseUdiskTypewhen'0'then'单机版安全U盘'when'1'then'企业版安全U盘'when'2'then'企业版管理盘'end, KBUdiskIDas'U盘金邦ID',CustomerNameas'客户',CfgNameas'配置', ProduceBatchas'生产批次号',ProduceRemarkas'生产备注'fromProduceUdiskKeyInfo ainnerjoinUdiskPolicyConfigInfo b ona.ConfigAu...
1、INNER JOIN && OUTER JOIN 2、CROSS JOIN 3、韦恩图 JOIN 全解 代码语言:javascript 代码运行次数:0 运行 AI代码解释 create tabletable_1(`id`INT(11)NOTNULL,user_namevarchar(20)NOTNULL)create tabletable_2(`id`INT(11)NOTNULL,user_namevarchar(20)NOTNULL)setsql_safe_updates=0;insert into ta...
3. JOIN语句练习 4. 判断函数--CASE 应用场景:自定义分组、统计有筛选条件的数量等 语法一: CASE 变量或要判断的字段或表达式 WHEN 常量1 THEN 要显示的值1(或语句1;) WHEN 常量2 THEN 要显示的值2(或语句2;) ... ELSE 要显示的值n(或语句n;) END...
sql server 多表连接 null sql多表join 题源来源与网络 你将斩获: 练练手,找找感觉 & 需求理解力 多表连接(事实表 + 维度表 + 维度表) 多对一:主表为事实表,待连接的表为维度表,left join,inner join 都可以; 锁定统计所需要的数据表和字段(绘制E-R图)【E-R图如何绘制,可以去百度 Workbeach 】...
The RIGHT JOIN command returns all rows from the right table, and the matching records from the left table. The result is NULL from the left side, when there is no match.The following SQL will return all employees, and any orders they might have placed:...
Left Join:returns all rows from thelefttable (table1), with the matching rows in the right table (table2). The result is NULL in the right side when there is no match. 左交:返回左表的所有行和匹配的右表的行,如果没有匹配上的用NULL. ...