EXISTS <= IN <= JOIN NOT EXISTS <= NOT IN <= LEFT JOIN 只有当表中字段允许NULL时,NOT IN的方式最慢: NOT EXISTS <= LEFT JOIN <= NOT IN 综上: IN的好处是逻辑直观简单(通常是独立子查询);缺点是只能判断单字段,并且当NOT IN时效率较低,而且NULL会导致不想要的结果。 EXISTS的好处是效率高,可...
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...
Example: SQL LEFT Join -- left join the Customers and Orders tablesSELECTCustomers.customer_id, Customers.first_name, Orders.amountFROMCustomersLEFTJOINOrdersONCustomers.customer_id = Orders.customer; Run Code Here's how this code works:
select * from t1 left join t2 on c1=d1 left join t3 on d2=e1 where e1=1; (e1满足非NULL条件,可以优化,甚至这里可以为:e2 in (select ……)) <==>等价于:select * from t1 left join t2 on c1=d1 inner join t3 on d2=e1 where e1=1; //inner转换 <==>等价于:select * from t1...
hivesql 多个left join inner join的执行顺序 hive left outer join,join操作innerjoin:只返回连接条件匹配上的数据outerjoinleft:左表为基准right:右表为基准full:左右两表数据都会查询出selecte.empno,e.ename,e.deptno,d.dnamefromempejoindeptdone.deptno=d.deptno
Join的类型 基本上有四种类型的连接,即Inner, Outer, Left and Right Join。每个提到的连接的解释如下。 Joins in SQL - Inner, Outer, Left and Right Join 1、Inner Join 让我们考虑以下两个表,第一个表的名称是Country(保存不同国家的id),另一个表的名称是State(保存这些国家/地区的各种状态)。
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 matches in the right table (Orders). ...
2.You JOIN the tablesgoalandeteamin an SQL statement. Indicate the list of column names that may be used in the SELECT line: 3.Select the code which shows players, their team and the amount of goals they scored against Greece(GRE). 4.Select the result that would be obtained from this ...
对应sql SELECT t.id, t.name, t.sex, t.head_img, t1.tel, t1.address AS userAddress, t2.province, t2.city FROM user t LEFT JOIN user_address t1 ON t1.user_id = t.id LEFT JOIN area t2 ON t2.id = t1.area_id WHERE ( t.id = ? AND t1.tel LIKE ? AND t.id > ?) ...
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