SQL开发实战系列(五):从执行计划看IN、EXISTS 和 INNER JOIN效率,我们要分场景不要死记网上结论 - 一、组合相关的行相对查询单表中的数据来说,平时更常见的需求是要在多个表中返回数据。比如,显示部门10的员工编码、姓名及所在部门名称和工作地址。select a.empno,a.d
SQL>select /*+ monitor */ SQL_ID, SQL_PLAN_HASH_VALUE, SQL_PLAN_LINE_ID, count(*)2 from T1 3 where T1.sql_id in (select T2.sql_id from T2) 4 group by SQL_ID, SQL_PLAN_HASH_VALUE, SQL_PLAN_LINE_ID 5 order by 1; SQL_ID SQL_PLAN_HASH_VALUE SQL_PLAN_LINE_ID COUNT(*)...
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=363 Card=1 Bytes=3) 1 0 SORT (AGGREGATE) 2 1 FILTER 3 2 TABLE ACCESS (FULL) OF 'BIG_TABLE' (Cost=363 Card=1011 2 Bytes=30336) 4 2 INDEX (RANGE SCAN) OF 'IDX_SMALL_TABLE' (NON-UNIQUE) ( Cost=1 Card=1 Bytes=3) Statistics --- 0 r...
AI代码解释 --SQL1:select/*+ monitor */SQL_ID,SQL_PLAN_HASH_VALUE,SQL_PLAN_LINE_ID,count(*)fromT1whereT1.sql_idin(selectT2.sql_idfromT2)group bySQL_ID,SQL_PLAN_HASH_VALUE,SQL_PLAN_LINE_IDorder by1;--SQL2:select/*+ monitor */SQL_ID,SQL_PLAN_HASH_VALUE,SQL_PLAN_LINE_ID,coun...
1、关于在 Oracle8i 时代中in和exists的区别这里有条SQL语句:select * from A where id in(select id from B) 以上查询使用了in语句,in()只执行一次,它查出B表中的所有id字段并缓存起来.之后,检查A表的id是否与B表中的id相等,如果相等则将A表的记录加入结果集中,直到遍历完A表的所有记录;它的查询过程类似...
Hello, select v_R_SYSTEM.ResourceID from v_R_System WHERE NOT EXISTS( select v_R_SYSTEM.ResourceID /* ,v_R_SYSTEM.ResourceType,v_R_SYSTEM.Name0,v_R_SYSTEM.SMS_Unique_Identifier0, v_R_SYSTEM.Resource_Domain_OR_Workgr0,v_R_SYSTEM.Client0,…
在云计算领域,SQL 查询的性能对于数据库管理和应用程序性能至关重要。为了改进 NOT EXISTS 查询的性能,可以采用以下策略: 1. 索引优化:确保在进行子查询的列上创建索引,以加快查询速度。...
SQL EXISTS Examples The following SQL statement returns TRUE and lists the suppliers with a product price less than 20: ExampleGet your own SQL Server SELECTSupplierName FROMSuppliers WHEREEXISTS(SELECTProductNameFROMProductsWHEREProducts.SupplierID = Suppliers.supplierIDANDPrice <20); ...
syntaxsql EXISTS( subquery ) Arguments subquery Is a restricted SELECT statement. The INTO keyword is not allowed. For more information, see the information about subqueries inSELECT (Transact-SQL). Result Types Boolean Result Values Returns TRUE if a subquery contains any rows. ...
Transact-SQL Syntax Conventions Syntax Copy EXISTS subquery Arguments subquery Is a restricted SELECT statement. The COMPUTE clause and the INTO keyword are not allowed. For more information, see the information about subqueries inSELECT (Transact-SQL). ...