Perform
We often have to look at the execution plan of an SQL statement in our actual work, for example:
After Sqlplus uses the command set autotrace on, the execution plan appears as follows:
SELECT STATEMENT optimizer=all_rows (cost=985 card=1
Top command:
The top command and the PS command have the same basic role of displaying the current process and other conditions of the system, but top is a dynamic display process that refreshes the current state with the user key. Such as? The
mysql| Security | Security MySQL Security Guide (2)
Release Date: 2000-5-10
Content:
--------------------------------------------------------------------------------
MySQL Security Guide (2)
Author: Yan Zi
2.1.3 Database and Table
CREATE TABLE T0
(
Sid int NOT NULL,
Sname VARCHAR2 (20)
)
Tablespace test;
--Loop Import data
Declare
MAXRECORDS constant int:=100000;
I int: = 1;
Begin
For I in 1..maxrecords loop
Insert into t0 values (i, ' Ocpyang ' | | i);
End Loop;
1. Speaking of MySQL, we immediately think of its small size, speed, but also open source features, so it is widely used. Today we summarize the most frequent two operations in MySQL: Inserts and queries, and the optimization method.
2. Insert:
3.
Oracle Virtual field 133. Currval and Nextval Create a sequence created SEQUENCE empseq for the table ...; SELECT Empseq.currval from DUAL; Inserts the numeric values of the sequence into the EMP values (empseq.nextval, ' LEWIS ', ' clerk ', 79
Abs: Get absolute value.
Acos: Gets the inverse cosine value.
Ada_afetch: Gets the return column of the database.
Ada_autocommit: Switch automatic change function.
Ada_close: Close Adabas D link.
Ada_commit: Alter Adabas D database.
Ada_connect:
This article mainly introduces the PHP array sorting code, the need for friends can refer to the following Code below: $val)////loop outputs the sorted key value pair { echo "$key = $valn";//output key value to } &NB Sp
The error of indexing using indexes six: indexing all columns
We know that indexing is an effort to improve query efficiency, but it should also be noted that indexes increase the cost of DML operations (INSERT, UPDATE, delete), and that most
Test
1. Create a user leonarding and grant DBA authority
Sys@leo> create user leonarding identified by leonarding default tablespace users;
Sys@leo> Grant DBA to leonarding;
2. Create a T-table, as long as the structure of information
Sys@leo>
Oracle 21. Replace distinct
with exists
when submitting a search that contains a list of multiple tables (such as the Department table and the employee table), avoid using distinct in the SELECT clause.
can generally consider using exist for
Today is the choice of sorting, including "Direct selection sort" and "heap sort."
The last time "bubble sort" was a quick row of abuse, and "Fast Platoon" won the reuse of Necoux, the natural envy of the brothers, the need to find a faster than
Recursive calls the number of recursive calls generated by the user or system;
DB block gets: The number of times the current chunk of data is requested;
Consitent gets gets the number of redo blocks of data from the buffer cache;
Physical reads
And then, in the previous example, set up two indexes on the table:
Sql> CREATE INDEX Ind_t_owner on T (OWNER);
The index has been created.
Sql> CREATE INDEX ind_t_id on T (object_id);
The index has been created.
For full table scans, use the
oracle| problem
Index is a common database object, it is set up and used properly, which greatly affects the performance of database applications and databases. Although there is a lot of data on the use of indexing, DBAs and Developer often deal
In Oracle databases, consistent gets is useful for judging the performance of a section of SQL, and generally comparing the performance of two segments of SQL is not to see whose execution time is short, but to see whose consistent gets small. But
Several features of the program are:
1: The Complete search engine
2: Three sorts of objects. (add time, download times, program name). and two sorts of sorting methods (reverse, order).
3: The administrator changes at any time.
4: Report link error.
Share An example of PHP array ordering, introducing and PHP, related knowledge, skills, experience, and some PHP source code, etc. The code is as follows: $val)////loop outputs the sorted key value pair { echo "$key = $valn";//output key value
The index database introduces the most frequent operation of the index user to the database is the data query. In general, a database needs to search the entire table for a query operation. When the data in the table is very large, it takes a long
Hints translated into Chinese is the hint, implied meaning, it is in the database role is to change the execution of SQL statements, you can use hints to force SQL in the way you set up to execute SQL, generally used to do performance diagnostics
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