问Oracle 11g："With Clause“非常慢EN最近学习Oracle，所以在Vm中配置一个win10的虚拟机来安装Oracle 11g，平时实验报告使用在虚拟机中使用SqlPlus，日常开发使用NaviCat进行连接，同时后期尝试安装多数据库和web服务搭建综合开发环境。 下载 Oracle官网下载地址 注册登陆Oracle账号，同意协议，选择Oracle Database 11g Release 2并选中下载Microsoft Windows (x64)...
第一种使用子查询的方法表被扫描了两次,而使用WITH Clause方法,表仅被扫描一次。这样可以大大的提高数据分析和查询的效率。 另外,观察WITH Clause方法执行计划,其中“SYS_TEMP_XXXX”便是在运行过程中构造的中间统计结果临时表。 语法: with tempName as (select ...) select ... --针对一个别名 with tmp as...
With语句可以在查询中做成一个临时表/View,用意是在接下来的SQL中重用,而不需再写一遍。 With Clause方法的优点: 增加了SQL的易读性,如果构造了多个子查询,结构会更清晰。 示例: withsoloempas(selectdistinctsalaryfromhy_emp)selectavg(salary)from(selectdense_rank()over(orderbysalary)asseq, dense_rank()ove...
We can also use the SQL-99 “WITH clause” instead of temporary tables. The Oracle SQL “WITH clause” will compute the aggregation once, give it a name, and allow us to reference it (maybe multiple times), later in the query. The SQL-99 “WITH clause” is very confusing at first b...
To keep it simple, the following example only references the aggregations once, where the SQL "WITH clause" is normally used when an aggregation is referenced multiple times in a query. We can also use the SQL-99 "WITH clause" instead of temporary tables. The Oracle SQL "WITH clause" will...
FUNCTION with_function(p_id IN NUMBER) RETURN NUMBER IS BEGIN RETURN p_id; END; SELECT with_function(id) FROM test WHERE rownum = 1 / WITH_FUNCTION(ID) --- 1 SQL> 有意思的是,当WITH子句中包含PL/SQL声明时,分号";"不再能用作SQL语句的终止符。如果我们使用它,SQL*Plus会等待更多命令文本...
select xm,zjh,dz,row_number()over(partition by zjh order by xm) 记录号 from cs 去重重复数据: with cs1 as (select xm,zjh,dz,row_number()over(partition by zjh order by zjh) 记录号 from cs)select * from cs1 where 记录号=1
Oracle allows you to use theUSINGclause to implicitly test for equality (=) when joining tables. Here’s the syntax of theLEFT JOINwith theUSINGclause: SELECTcolumn_listFROMXLEFTJOINYUSING(id);Code language:SQL (Structured Query Language)(sql) ...
SUM(quantity * unit_price) totalFROMorder_itemsGROUPBYorder_id;Code language:PostgreSQL SQL dialect and PL/pgSQL(pgsql) Here’s the result set: order_idtotal 729267.81 1139687.59 2090695.37 To retrieve only orders with a total greater than30,000, you use aGROUP BYclause: ...
private SQL areas associated withopen cursors. If the private SQL areas for all concurrently open cursors fillsyour available memory so that there is no space for a new SQL statement, thenthe statement cannot be parsed. Oracle Database returns an error indicatingthat there is not enough memory....