mysql join multiple tables

Today, the user responded to a CI list page and opened it very slowly. View Code It is found that the SQL statement used to load the list is composed of multiple left join tables. Select nm. ID, nm. model_id, NMM. code, nm. serialcode, nm. manufacturer, nm. maintainer, nm. state, nm. type, nm. deleted, nm. remark, DP. DeviceID, D. Name as d_name, DP. portname, I

user.Because on will filter out non-conforming rows first, then other operations will be performed, so on is arguably the quickest.On multi-table queries, on is more effective than where. The system first synthesizes a temporary table based on the conditions of the joins between the tables, then the where is filtered, then calculated, and then filtered by having. Thus, to filter the conditions to play the right role, first of all to understand when t

Today, while doing a mini-letter wall lottery program, I encountered a problem, I need to query the difference set of scale, the business situation is this A table is used to save lottery users (www.111cn.net a person may have more than one piece of data), while the other table is saved by the winning users, I need to report the winner of the user to find out, just start with a where to do a multiple table association query, But it turns out that whe

Diversity and multi-data source problems using reporting tools such as jasperreport are not easy to handle, such as displaying MongoDB and MySQL hybrid operations. Although Jasperreport/birt has features such as virtual data source or table join, but only in the commercial or high-end version, it is very difficult to implement in the free version, and the function has a large limitation, it is impossible to

index page each time the function is called, this is a very performance-consuming operation, and for many other relational databases it is using "histogram" statistics to avoid this operation ( I believe that the MARIADB subsequent version will also implement histogram statistics.2.3 Choice of order and access mode: Poor lift MySQL finds the optimal execution order and access mode by enumerating all the left-deep trees (or all the left-deep trees ar

Use connection (join) instead of subquery (sub-queries)MySQL supports SQL subquery starting from 4.1. This technique can use the SELECT statement to create a single-column query result, and then use the result as a filter for another query. For example, if we want to delete a customer who does not have any orders in the customer's basic information table, we can take advantage of the subquery to remove all

data in that result set by using the data in the resulting dataset as a filter to the next table, and then merges the results. If there is a third participating join, then the join result set of the previous two tables is used as the base data for the join, once again querying the data by looping through the criteria

I don't know if anyone has encountered such a disgusting problem: two tables are connected to the query and limit. SQL is very efficient. However, after order by is added, the statement execution time has become very long, extremely low efficiency.This is the case: there are two tables, team table and people table. Each people belongs to a team and there is a field team_id in people.The following table crea

How to use PHP MySQL lock tables MySQL table lock lock tables feel like a closed space When MySQL discovers the lock tables command, it takes the table with the lock tag into the enclosing space until the unlock

Differences between Mysql sub-tables and partitions bitsCN.com I. What are mysql table shards and partitions?What is table sharding? on the surface, it means dividing a table into N small tables. for details, see the three methods of mysql table sharding.What is a partition?

, tombstone Isdelete bit default 0 eliminate duplicate rows distinct: Use distinct before columns in select to eliminate duplicate rows Aggregation Functions Count (*) Mid (column) max (column) AVG (column) sum (column) Group: GROUP By field, indicating that the same data in this field is placed in a group Having is the filtering of data after grouping Connection Query when the columns of the query result are from multiple

Mysql exercises ---- The JOIN operation, ---- thejoin Game Id Mdate Stadium Team1 Team2 1001 8 Jun 2012 National Stadium, Warsaw POL GRE 1002 8 Jun 2012 Stadion Miejski (Wroclaw) RUS CZE 1003 12 Jun 2012 Stadion Miejski (Wroclaw) GRE CZE 1004 12 Jun 2012 National Stadium, Warsaw POL RUS

.5. mysqldiff In fact, permission and table change are low-frequency operation events. Although the above four methods can achieve the goal, they are essentially resource-consuming operations. with this in mind, we can track permissions and table structure changes by comparing them. For details, see sys-mysql-diff. considering the versatility, the sys-mysql-diff tool needs to obtain the definition statement