TheNOT INoperator in SQL is used to fetch all the records that aren’t present based on a particular field. We can use this operator to select records from one table that aren’t present in another table: SELECT * FROM Course c WHERE c.id NOT IN ( SELECT r.course_id FROM Registratio...
例如: 表 TAB1 16,384 条记录表 TAB2 5 条记录,选择TAB2作为基础表 (最好的方法) select count(*) from tab1,tab2 执行时间0.96秒,选择TAB2作为基础表 (不佳的方法) select count(*) from tab2,tab1 执行时间26.09秒; 如果有3个以上的表连接查询,那就需要选择交叉表(intersection table)作为基础表,...
一个Table存储一个类别的数据,每一行是一条数据,每一列是这种数据的一个属性; Table就像一个二维的表格,列(columns)是有限固定的,行(rows)是无限不固定的,如: 试水 1、movies为表名,选取某列全部内容 1 SELECTtitleFROMmovies 2、按Id(某列的值选取行) 1 SELECTtitle, directorFROMmoviesWHEREId < 5 3、...
chain_cnt :Number of rows in the table that are chained from one data block to another or that have migrated to a new block, requiring a link to preserve the old rowid. This column is updated only after you analyze the table. 数据缓冲区命中率(百分比小于90就要加大db_cache_size) 查询V$S...
The SELECT INTO has an ON filegroup clause where you can specify what file group to store the new table on. This does not apply to temporary tables. This involves 2 steps: Create the table based on the SELECT statement Insert the rows from the results of the SELECT statement ...
5rowsinset(0.01sec) Great[test]>deletefromtt1 ->whereid=5 ->andc1isnotnull -> 当我输入完上面的SQL时,发现逻辑未考虑全,不想执行这个SQL了,怎么办呢?这里有好几种解决办法:你可以ctrl+c 终止命令的执行,也可以关闭当前的mysql客户端,甚至关闭操作命令的电脑。然后有一种标准且简单的方式,就是在命令的...
where not in another in SQL Server--- select * from table 1 where ids not exist in table 2...
GO SELECT * FROM TestBatch; -- Returns no rows. GO 在下面的示例中,第三个 INSERT 语句产生运行时重复主键错误。 由于前两个 INSERT 语句成功地执行并且提交,因此它们在运行时错误之后被保留下来。 SQL 复制 CREATE TABLE TestBatch (ColA INT PRIMARY KEY, ColB CHAR(3)); GO INSERT INTO TestB...
SELECT*FROMCustomers ORDERBYCustomerNameDESC FETCHFIRST3ROWS ONLY; Exercise? What would the following query do in SQL Server? SELECT TOP 5 * FROM Customers; Select the first 5 records from the Customers table Select the last 5 records from the Customers table ...
statement to retrieve all the records in a table regardless if some values repeat or not. If you wish, you can use the DISTINCT keyword to remove duplicates from your results. For instance if you wanted to just return a unique list of employees’ titles you would use this SQL SELECT ...