mysql query order by

MySql database query results use a table to output PHP code samples, mysql query results In general websites, we usually see that the table data in many databases is displayed in the table in the browser. It is amazing at first, but it is not too complicated to think about it carefully, since dql and dml can be returne

MySQL query too slow is a very annoying thing, so, the author has spent some time to organize the MySQL Query speed optimization program, this article is all the author's personal views, such as questions or wrong welcome to communicate and correct, we learn together progress. Count () Optimization for

The example in this article describes the method by which Php+mysql counts the number of records in each table in the library and in descending order. Share to everyone for your reference, as follows: This is a simple code that implements the ability to count the number of records in each table in the database, and to sort in descending order $host = ' 127.0.0.

Label:Logical query processing steps for the execution of the SELECT statement:(8) SELECT (9) DISTINCT(one) (1) From (3) (2) on (4) WHERE (5) GROUP by (6) with {CUBE | ROLLUP}(7) Having (10) ORDER by 1.FROM2.ON3.JOIN4.WHERE5.GROUP by6.WITH CUBE or with ROLLUP7.HAVING8.SELECT9.DISTINCT10.ORDER by11.TOPMicrosoft points out that the actual physical execution

Tags: http knowledge point error variable coin lock table response Long MYQLLogs in MySQL include: error log, binary log, General query log, slow query log, and so on. Here is the main introduction of the more commonly used two features: General query log and slow query log.

Label:The end of the paper is shallow 1. What do you need to know about the database as a developer? In the development of the database, basically only the SQL statements, how to write SQL and optimize it is more important, those MySQL thick book for the DBA, we just need to learn the SQL in it. 2. Since writing SQL is a goal, how can you write sql well. Learn the following points: 1) The execution order of

Today, I found in mysql that there is such a select * from bb order by null sentence that cannot be seen, later, I found out that order by null is used to forcibly disable sorting of query results. Order by null is used to forcibly disable sorting of

Tags: es2017 paste efficiency doc share INI image technology share DirectData volume, 13 million of tables plus 1.12 million of tablesNote: This article is only part of the optimization, not comprehensive, for reference only, welcome guidance.Please take a look at Tim to see, because when writing in Tim, paste over there is a problem, directly on the link.Https://823948977.docs.qq.com/T5e6dBYLoZz?opendocxfrom=timThe article is similar in content:MySQL Tens data

Mysql fuzzy query optimization and mysql fuzzy query First, create an index for the fields to be searched in the database (mysql index is unfamiliar, please refer to here ). Secondly, use the following function for fuzzy search. If the position is greater than 0, it indicate

Last time we introduced: Suitable for beginnersMySQLFor more information about the usage of SELECT statements for learning notes, we will introduce some suitable MySQL learning notes for beginners.Order by clauseNext, let's take a look at this part. Sort results by order by clause The order by clause sorts the query re

Recently because of the need to study the MySQL random extraction implementation method. For example, to randomly extract a record from the TableName table, the general wording would be: SELECT * from TableName ORDER by RAND () LIMIT 1. However, I later looked at the official MySQL manual, where the hints for rand () probably meant that the rand () function cou

the fields to be computed, then the results are the same, except where the Rushmore technique can be used, and the having is not, the latter is slower in speed.If a calculated field is to be involved, it means that the value of the field is indeterminate before it is calculated, where the action time is done before the calculation, and having is calculated before it works, so in this case the results will be different.On a multi-table join query, on

user_info> user_info.dat 7. export data Select_statment into outfile "dest_file "; For example: The code is as follows: Select cooperatecode, createtime from publish limit 10 bytes outfile "/home/mzc/temp/tempbad.txt "; 8. import data Load data infile "file_name" into table table_name; For example: The code is as follows: Load data infile "/home/mzc/temp/tempbad.txt" into table pad; 9. splice the data in the two tables and insert them into the other table. The following example shows how to spl

Recently, we have studied the implementation of MYSQL random extraction. For example, to randomly extract a record FROM the tablename table, the general syntax is: SELECT * FROM tablename order by rand () LIMIT 1.However, I checked the MYSQL official manual. The prompt for RAND () indicates that the RAND () function cannot be used in the

Reprinted from: http://blog.csdn.net/jintao_ma/article/details/512533561. What do you need to know about the database as a developer? In the development of the database, basically only the SQL statements, how to write SQL and optimize it is more important, those MySQL thick book for the DBA, we just need to learn the SQL in it.2. Since writing SQL is a goal, how can you write sql well. Learn the following points:1) The execution

WHERE key2=constant ORDER BY key_part2; * Both ASC and DESC are used: SELECT * FROM t1 ORDER BY key_part1 DESC, key_part2 ASC; * The index keys used to search for records are not the same as the order by: SELECT * FROM t1 WHERE key2=constant ORDER BY key1; * There are many tables connected together, and the fields

need to index a long string, the index takes up a lot of space, you can usually index the beginning of some characters to save the index space, improve index efficiency, but also reduce the selectivity of the index. Selectivity of index = total number of records of the index value/data table are not duplicated. The higher the selectivity of the index, the higher the query efficiency. multicolumn indexes: First you need to explain that creating inde

of WHERE + order by, for example: Copy codeThe Code is as follows: SELECT [column1], [column2],... FROM [TABLE] WHERE [columnX] = [value] order by [sort]; Create a joint index (columnX, sort) to optimize order. NOTE: If columnX corresponds to multiple values, the following statement cannot optimize order by using ind

MySQL Query Optimization: Use a subquery instead of a non-primary key to connect to the query instance to introduce bitsCN.com one-to-many two tables. Generally, the foreign key of one table is associated with the primary key of another table. However, there are also some unusual situations, that is, two tables are not joined by the primary key of one of the tabl

A problem occurred while using order by today. I found that the previous understanding of ORDER BY is incorrect. I saw the order by usage on the w3s website and thought it was to sort the selected data in ascending or descending ORDER of the keywords. When I tried to select the dataset data today, it is found that the