Select Statement In Sql With Multiple Where Clause

Designing 1 applications doesn't seem to be difficult, but it's not easy to achieve the optimal performance of the system. There are many choices in development tools, database design, application structure, query design, interface selection, and so on, depending on the specific application requirements and the skills of the development team. This article takes SQL Server as an example, discusses the application performance optimization techniques from the perspective of the background database, and gives some useful suggestions. 1 database design to achieve optimal performance in a good SQL Server scenario, the key is to have 1 ...

We want to do not only write SQL, but also to do a good performance of the SQL, the following for the author to learn, extract, and summarized part of the information to share with you! (1) Select the most efficient table name order (valid only in the Rule-based optimizer): The ORACLE parser processes the table names in the FROM clause in Right-to-left order, and the last table in the FROM clause (the underlying table driving tables) is processed first, In the case where multiple tables are included in the FROM clause, you must select the table with the least number of records as the underlying table. If...

Method 1 delete yourtable where [id] not in (select max ([id]) from yourtable group by (name + value) b on a.id = b.id where b.id ...

SQL statement for querying and deleting duplicate records (i) For example, there is a field "name" in Table A, and the "name" value may be the same between different records, and now you need to query between the records in the table, the "name" value has duplicates, and select name, Count (*) from-a group by name has count (*) > 1 as ...

A few suggestions to improve SQL execution efficiency: Try not to include subqueries in where; queries about time, try not to write: where To_char (dif_date, ' yyyy ') =to_char (' 2007-07-01 ', ' yyyy '); In the filter condition, the condition in which the maximum number of records can be filtered must be placed at the end of the WHERE clause, and the last table (underlying table, driving table) in the FROM clause will be first ...

In our development of the efficiency has been a problem, especially for a lot of large data operations, today we ran into a random query data, at first we may think of the simplest order by RAND () to operate but the efficiency is not flattering ah. 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 is: SELECT * from TableName ORDER by RAND () LIM ...

Using hive, you can write complex MapReduce query logic efficiently and quickly. In some cases, however, the Hive Computing task can become very inefficient or even impossible to get results, because it is unfamiliar with data attributes or if the Hive optimization convention is not followed. A "good" hive program still needs to have a deep understanding of the hive operating mechanism. Some of the most familiar optimization conventions include the need to write large tables on the right side of the join, and try to use UDF instead of transfrom ... Like。 Here are 5 performance and logic ...

select * from table limit [offset,] rows | rows offset The offset clause clause can be used to force a select statement to return the specified number of records. limit Accepts one or two numeric parameters. The parameter must be an integer constant. Given two parameters, the first parameter specifies the offset of the first record row, and the second parameter specifies the maximum number of record rows to return. The offset of the initial record line is 0 (not 1): ...

Mysql limit usage: When we use the query, often to return to the first few or a few lines in the middle of the data, how to do this time? Do not worry, mysql has provided us with such a function. SELECT * FROM table LIMIT [offset,] rows | rows OFFSET & nbs ...