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1 SQL statement multi-table query For example, query employees (employee table) and departments (department table) information according to department_id.   Mode 1 (Universal): SELECT... FROM... WHERE SELECT e.last_name,e.department_id,d.department_name FROM employees e,departments d where e.department_id = d.department_id  ...

Understanding Oracle's execution plan is the first step in optimizing, so let's start with the example below. Additional information below 1. Create test tables [sql] view plaincopy   SQL> create table t as select 1 id,object_name from dba_objects;           Table created           SQL> update t set id=99 where rownum=1;           1 ...

title: Server Development Series 2 date: 2017-9-13 11:27:46 After three weeks of crazy overtime, the pace of server development can finally be put on hold, and there is time to take a good look at the project from an "external" perspective. Write tcp server naked using swoole In the absence of the Swiss Army Knife (familiar framework) ...

Tool preparation ​JDK Since it is a Java protocol, JDK is essential, but the largest version of JDK supported by lr11 is only jdk1.6, and it must be 32 bits. ​ jdbc connects jar packages To connect to oracle database, you need to prepare the database-driven jar package and select the corresponding version of the jar package acc ...

Change from: http://mysql.taobao.org/monthly/2016/06/07/ External Temporary Table Through CREATE TEMPORARY TABLE Create temporary tables, which are called external temporary tables. This temporary table is only visible to the current user and closes automatically at the end of the current session. This temporary table can be named with the ...

The first condition for efficient index use is to know what queries will be used in the index. This problem is related to the "Leftmost Prefix Principle" in B+Tree. Here is an example to illustrate the Leftmost Prefix Principle. Let's start with the concept of joint indexing. In the above, we all assume that the index refers to only ...

Previous review Subquery The missing distinct having where sub-query in subquery between and multi-table query Query results use multi-table data Left join query left join on Right join query right join on Full join query full join on Inner join on Previous review order by select * from `group` order by max_size; ...

Example: 　　 #sqlplus /nolog 　　SQL> conn / as sysdba; 　　create user username identified by password; 　　grant connect,resource to username; 　　grant select,insert,update,delete on Table name to username; 　　//Let this user create views 　　grant CREATE VIEW to username; 　　//Let this user create tables 　　grant create table to ...

I. An Overview of Join's Grammar join is used to link fields in multiple tables. The grammar is as follows: ... FROM table1 INNER|LEFT|RIGHT JOIN table2 ON conditiona Table 1: left table; table 2: right table. JOIN can be roughly divided into three categories according to its functions: INNER JOIN (inner join, or equivalent join) ...

function Grammar for Defining Functions Practice calculating the sum of two numbers Adding Data to Exercise Functions Call function of exercise function view Characteristics of Views Adding and deleting views Add view Delete view Synonym SYNONYM grammar Practice synonyms cursor Classification of cursors Cursor syntax Pr ...