SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate FROM Orders LEFT OUTER JOIN Customers ON Orders.CustomerID = Customers.CustomerID; 参考链接 SQL JOINs Explained W3Schools SQL JOIN Tutorial 通过这些基础概念、类型、应用场景以及解决方案,你应该能够更好地理解和处理SQL连接问题。相关...
SELECT*FROMtable1FULLOUTERJOINtable2ONtable1.column=table2.column; 1. 2. 3. 5. CROSS JOIN The CROSS JOIN returns the Cartesian product of the two tables, which means it combines each row from the first table with every row from the second table. SELECT*FROMtable1CROSSJOINtable2; 1. 2...
INNER JOINs: An inner JOIN is a filtered form of the cross JOIN, in which only the tuples of both output tables that fulfil the selection condition defined by the user are combined in the results. OUTER JOINs: The outer JOIN is an extension of the inner JOIN result and contains the ...
1) 交叉联结:cross join 也叫笛卡尔积 英文名称cross join 案例: 表一三行数据 跟 表二两行数据进行交叉联结 表一cross join 表二 的数据表 为3行*2行=6行数据 类似扑克牌 13张牌=(A.2.3.4.5.6.7.8.9.10.J.Q.K) 花色=(♠.♥.♦.♣) 13张牌X花色=13*4=(52张扑克牌) 平常用的比较少 ...
1、交叉联结 cross join 表1中的每一行与表2中的每一行逐行联结,得到的联结后的表的行数=表1的行数*表2的行数 交叉联结是所有联结的基础,但由于联结后的行数较多,在实际应用中使用较少。 2、内联结 inner join 查找出同时存在于两张表中的数据,即两个表重叠的部分 ...
2.1 交叉联结(笛卡尔联结)cross join 表中的每一行都与另一张表的每一行合并在一起。在实际运用中比较少,结果行数太多需要花费大量的运算成本和设备的支持,交叉结果行数太多没有实际的价值。这是为了更好理解后面的联结。 2.2 内联结 inner join 同时查找出同时存在于两张表的数据,然后通过交叉联结显示。
The size of the SQL standard grew significantly between 1992 and 1999. The SQL-92 standard had almost 600 pages, but it was still accessible to regular SQL users. Books likeA Guide to the SQL Standardby Christopher Date and Hugh Darwen discussed and explained the SQL-92 standard. ...
42、b.matchid13、Listeverymatchwiththegoalsscoredbyeachteamasshown.Thiswilluse"CASEWHEN"whichhasnotbeenexplainedinanypreviousexercises.*/SELECTa.mdate,a.team1,sum(CASEWHENb.teamid=&team1THEN1ELSE0END)asscore1,a.team2,sum(CASEWHENb.teamid=&team2THEN1ELSE0END)asscore2FROMgameasaleftJOINgo ...
Log truncation explained There's a difference between truncating a transaction log and shrinking a transaction log. Log truncation occurs normally during a transaction log backup, and is a logical operation that removes committed records inside the log, whereas log shrinking reclaims p...
(This process is explained in more detail in View Resolution.) As long as the set of hints that exists on the underlying tables of the view are identical to each other, the query is eligible to be matched with an indexed view. Most of the time, these hints will match each other, ...