hive query optimization

Common query optimization 1:max () Optimization: Adding indexes to the corresponding columns2:count () Optimization: COUNT (*) calculates the number of containing null records, and COUNT (Field_name) contains only the number of Nulls (this is also the reason why the results of the two count methods are inconsistent),

MySQL query optimization: profile function MySQL query optimization: profile function. Note that you need to install the profile module. 1. The version is later than 5.0.37. (Show profiles and show profile were added in MySQL 5.0.37 .) SELECT @ profiling;To check whether the profile has been enabled. If the profilng va

This article describes Oracle's query optimizer, a key component of the database, which gives Oracle users excellent performance. Oracle's query optimization technology is unmatched in functionality, and this article discusses all the important areas of query optimization in

We all know that in MySQL database query optimization, the actual application of the database {for example, MySQL (the best combination with PHP)} means the actual operation and use of related tools. Using indexes and using EXPLAIN to analyze queries and adjust the internal configuration of MySQL (the best combination with PHP) can optimize queries. Any database program We all know that in MySQL database

copy of the original table, but in fact each server has only one member table and a distributed partition view. The data location is transparent to the application.11. Rebuild the index DBCC reindex, DBCC indexdefrag, shrink data and log DBCC shrinkdb, and DBCC shrinkfile.Set automatic log shrinking. Do not set Automatic database growth for large databases, which will reduce server performance. T-SQL is very well written. The following lists common points:First, the DBMS processes the

disadvantages of this approach are almost identical to "test three" , except that the first generation of execution plans is not affected by the parameters.The following two stored procedures, after the creation of a stored procedure, no matter who executes first, the query plan is the same!EXEC P_test2 @ProductID = 870EXEC P_test2 @ProductID = 897This is the real use of the so-called "parameter sniffing"! When the

In general, Oracle databases operate more efficiently than SQL Server databases in large data environments. From the query optimization alone, the two are quite different. Below, the author of the database query optimization of the difference to do a description, if there is not accurate place, but also please criticiz

storing the time with a string, and storing the IP address with an integer data type. (3) Try to avoid null: The column should be specified as NOT NULL unless you want to store null. In MySQL. Columns that contain null values are very difficult to query optimization. Because they make indexes, index statistics, and comparison operations more complex. You should replace the null value with 0, a special valu

This paper summarizes and analyzes the techniques of MySQL query optimization. Share to everyone for your reference, specific as follows: People who are familiar with SQL statements know that if you want to operate on a task, the SQL statement can have a lot of relevant writing, but different ways of writing query performance may be a great difference. This art

Anyone familiar with SQL in MySQL's five query optimization methods knows that SQL may write a variety of statements to complete the same task, but the query performance of different statements may be quite different, this article lists five query optimization methods. of co

Query optimization on SQL statements. The foreground application works on the database server, and ultimately relies on the SQL statements in the application. According to incomplete statistics, SQL statements consume about 80% of the database server's resources. Therefore, how to improve the execution efficiency of SQL statements is a problem that must be considered in database

, MySQL will not log slow query How to turn on slow query: 1. Close the current MySQL service: net stop MySQL 2, start through Safe mode will write log. 3. Turn off MySQL with Safe mode activated 4, set the time of the slow query to 0.5 seconds, set long_query_time=0.5 5. Select * FROM table where xx= ' 00 '; 6, go to the slow

This article describes how to optimize MySQL database queries in three ways. We all know that during the actual MySQL query optimization process, database applications, such as MySQL (the best combination with PHP), mean the operation and use of the tool. Using indexes, using EXPLAIN to analyze queries, and adjusting the internal configuration of MySQL (the best combination with PHP) can optimize queries. A