我的程序如下: --/ CREATE OR REPLACE procedure Update_TB_INTERACTLOG IS BEGIN FOR records in (select TNAME from tab where TNAME like 'TB_INTERACTLOG%' and TABTYPE = 'TABLE') LOOP dbms_output.put_line(records.TNAME||' modified'); END LOO 浏览2提问于2012-07-30得票数 0 回答已采纳 ...
EXISTS(W3schools) The EXISTS operator is used to test for the existence of any record in a subquery. The EXISTS operator returns TRUE if the subquery returns one or more records. 1. 2. 3. 基本型: SELECT c1 FROM t2 WHERE EXISTS (SELECT c2 FROM c2 WHERE condition); 1. 2. 3. 本质:...
The IS NULL operator is used to test for empty values (NULL values).The following SQL lists all customers with a NULL value in the "Address" field:ExampleGet your own SQL Server SELECT CustomerName, ContactName, AddressFROM CustomersWHERE Address IS NULL; Try it Yourself » Tip: Always...
SELECTCustomers.CustomerName, Orders.OrderID INTOCustomersOrderBackup2017 FROMCustomers LEFTJOINOrdersONCustomers.CustomerID = Orders.CustomerID; Tip:SELECT INTOcan also be used to create a new, empty table using the schema of another. Just add aWHEREclause that causes the query to return no data...
,可以使用SELECT语句来实现。SELECT语句用于从数据库中检索数据,并可以通过WHERE子句来添加条件。 以下是一个示例的SELECT语句,用于从表中选择特定列的值: 代码语言:txt 复制 SELECT column_name FROM table_name WHERE condition; 其中,column_name是要选择的列名,table_name是要查询的表名,condition是要应用的...
in/exists 对比 in 是把外表和内表作 hash 连接,而 exists 是对外表作 loop 循环,每次 loop 循环再对内表进行查询; 如果查询语句使用了 not in 那么内外表都进行全表扫描,没有用到索引; 而 not extsts 的子查询依然能用到表上的索引; 所以无论那个表大,用 not exists 都比 not in 要快。 **between...
1. A general nested loop to go forward one by one DECLARE @Class int, @Score int; DECLARE cursor_product CURSOR LOCAL FAST_FORWARD READ_ONLY --fastest configFOR SELECT class, score FROM #Student; OPEN cursor_product; FETCH NEXT FROM cursor_product INTO @Class,@Score; --must have! WHILE...
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例如,从 MySQL 8.0.18 开始以下查询可以使用 hash join 进行连接查询: SELECT * FROM t1 JOIN t2 ON t1.c1=t2.c1; Hash join 不需要索引的支持。大多数情况下,hash join 比之前的 Block Nested-Loop 算法在没 分享回复赞 万树it学院吧 归鸿不语2016 万树IT:程序员必须注意的十大编程禁忌程序员在编程的...
I got basic SQL JOIN knowledge and just verified them in http://www.w3schools.com/sql/default.asp. For example: SELECT Employees.Name, Orders.Product FROM Employees INNER JOIN Orders ON Employees.Employee_ID=Orders.Employee_ID In this above query, having same fieldname: Employee_ID in ...