SQL会将IN语句转换成多个表的连接,如果转换不成功则先执行IN里面的子查询,再查询外层的表记录,如果转换成功则直接采用多个表的连接方式查询。由此可见用IN的SQL至少多了一个转换的过程。一般的SQL都可以转换成功,但对于含有分组统计等方面的SQL就不能转换了。 推荐方案:在业务密集的SQL当中尽量不采用IN
2.When any type of join is processed, PROC SQL starts by generating a Cartesian product, which contains all possible combinations of rows from all tables.In all types of joins, PROC SQL generates a Cartesian product first, and then eliminates rows that do not meet any subsetting criteria tha...
1、自连接(join 等同于inner join ):查询结果为两边都存在的数据 2、左连接 left join :返回左边全部数据,右边存在返回,不存在为null 3、 右连接 right join :返回右边全部数据,左边存在返回,不存在为null 4、 全连接 full join :只要某个表中存在就返回,另一个不存在为nul SELECT d.*FROM depart_info d...
select * from Customer cswhere cs.Group_No = '册本编号' andcs.Customer_No not in ( select Customer_No from Customer cs left join Meter me on cs.Customer_No = me.Customer_No inner join Meter_data md on me.meter_no = md.meter_no and md.date = '2019-04-09' where cs.Group_NO=...
从执行计划看NOT IN、NOT EXISTS 和 LEFT JOIN效率,记住内外关联条件不要乱放-SQL开发实战系列(六) - 一、从执行计划看NOT IN、NOT EXISTS 和 LEFT JOIN效率有些单位的部门(如40)中一个员工也没有,只是设了一个部门名字,如下列语句:select count(*) from dept where
The SQL LEFT JOIN clause is a powerful feature in SQL used to combine records from two tables based on a related column. The LEFT JOIN keyword ensures that all rows from the left table (the first table listed) are returned, along with the matched rows from the right table. If there is...
LEFT JOIN right_data_table ON left_data_table.key_variable = right_data_table.key_variable; QUIT; ``` 在上面的例子中,使用PROC SQL语句执行一个左连接操作。left_data_table和right_data_table是要连接的两个数据集,key_variable是作为连接条件的变量。 LEFT JOIN操作将返回left_data_table中的所有记录...
ExampleGet your own SQL Server SELECTCustomers.CustomerName, Orders.OrderID FROMCustomers LEFTJOINOrdersONCustomers.CustomerID = Orders.CustomerID ORDERBYCustomers.CustomerName; Try it Yourself » Note:TheLEFT JOINkeyword returns all records from the left table (Customers), even if there are no ma...
Left Anti Join in SQLJason_2021 1 Reputation point Aug 19, 2021, 7:47 PM I’m trying to write a query that looks at an “attendance table” for a given date (such “Last Week”) to see if a person has attended to a certain location in the past or if they are a first timer....
proc sql;select one.x, a, b /*select one.* , b* one.*表⽰表one中所有的列/ from one, two where one.x = two.x;quit;3.1：在标准内连接中，出现两个表都含有重复的值的情况，内连接会对所有满⾜条件的观测⾏进⾏⼀⼀对应的笛卡尔积 4：Outer Join You can think of an outer...