complex sql queries tutorial

Oracle Notes (eight) complex queries and summariesOne, complex query1. List all department numbers and names of at least one employee and count the average wage, minimum wage and maximum wage of these departments.1. Determine the required data sheet: EMP Table: Can find out the number of employees; Dept Table: Department name; EMP Table: Statisti

Tags: Oracle SQL face question query selectWhen the query to the results of complex processing, you can use the union query, sub-query, etc. to get the desired results. The following is a specific classic question, hoping to inspire readers. 1. Title Requirements: Table NBA records the team Name and year of the winning team: TEAM year--------------------------------------------------Piston 1990Bull 1991Bu

remaining records in the right table at the same time) select * from CUSTOMER C outer join ORDERS O on c.id=o.customer_id;2) subquery (nested query) subquery: SELECT * from O Rders where customer_id= (select ID from customer where name= ' Zhang San '); 3) union query select * FROM orders where price>200 UNION Sele CT * from Orders WHERE customer_id=1; Take a set of two statements. and remove the repeated records. Ii. paging in the database: 1) pages in MySQL: (LIMIT m,n Note: M indicates the st

MySQL allows storage results to be paged for complex queries. It seems that few people are talking about paging, are we all addicted to limit m,n?In the case of indexing, limit m,n speed is sufficient, but when searching for complex conditions,where somthing ORDER by Somefield+somefieldMySQL searches the database for "all" qualifying records, and then takes out t

IntroductionSee a popular blog today. NET Senior Engineer face questions of SQL, asked to find the highest score of each department, and by the department number, the student number in ascending order. This query is more complex, but also more typical, since the use of ORM, a long time did not write SQL statements, so I studied the next, I also wrote a: With Cte1

PrefaceMyBatis, as we all know, the semi-automatic ORM framework, originally called Ibatis, and later seemed to be the 10 Apache software fund hosting it to Goole Code, renamed the MyBatis, the function is more powerful than before. It's a relatively fully automatic, durable framework hibernate, more flexible and lightweight, which I still have a deep understanding of.One of the powerful features of MyBatis is the dynamic SQL capability, can save us a

can ensure that the database will faint. In addition, execution plans can be reused, and the simpler SQL statements are more likely to be reused. Complex SQL statements have to be re-parsed as long as one character changes, and then the bulk of the garbage is stuck in memory. It is conceivable how inefficient the database will be. 4. Staging intermediate results

that the database will faint.In addition, execution plans can be reused, and the simpler SQL statements are more likely to be reused. Complex SQL statements have to be re-parsed as long as one character changes, and then the bulk of the garbage is stuck in memory. It is conceivable how inefficient the database will be.4. Staging intermediate results using tempor

Label:IntroductionSee a popular blog today. NET Senior Engineer face questions of SQL, asked to find the highest score of each department, and by the department number, the student number in ascending order. This query is more complex, but also more typical, since the use of ORM, a long time did not write SQL statements, so I studied the next, I also wrote a: w

person's resolution is worse, if people are looking dizzy, I can ensure that the database will faint.In addition, execution plans can be reused, and the simpler SQL statements are more likely to be reused. Complex SQL statements have to be re-parsed as long as one character changes, and then the bulk of the garbage is stuck in memory. It is conceivable how ineff

=half_million.counter);QUERY PLAN______________________________________________________________Merge Join (cost=4.12..37650.65 rows=500000 width=42)(actual time=0.033..3272.940 rows=500000 loops=1)Merge Cond: (one_million.counter = half_million.counter) -> Index Scan using one_million_counter_idx on one_million (cost=0.00..32129.34 rows=1000000 width=37) (actual time=0.011..694.466 rows=500001 loops=1) -> Index Scan using half_million_counter_idx on half_million (cost=0.00..14120.

. In the third step, the sub-bar checks to find out which table query is slow, or which condition causes the query to be slow. The fourth step, with the SQL execution plan, this because they are not good at looking at execution plan, can only try to avoid full table scan, early limit the scope of SQL data filtering. The fifth step is to check if an inappropriate in query is used, and the excess in will resu

SQL query beginner's Guide Reading Notes (2) Creating SQL queries, beginner's guide SQL PARTII: SQL Basics CHAPTER 4 Creating a Simple Query This section describes how to create an SQL statement: "Request/Translation/CleanUp/

analysis software to locate the slow query statement has completed the SQL optimization of the more than half. Next, you can see why the SQL query is slow by looking at the slow query statement by executing the explain or desc command in MySQL.Mysql> Explain select * from test.t \g*************************** 1. Row *************************** id:1 select_type:simple table:t Type:A

The Standard Edition and Enterprise Edition editions of SQL Server 2000 provide the complex retrieval feature of strings in table data-full-text searches ). This feature needs to be added through custom installation options during installation. 10.7.1 full-text index and Directory Full-text search is implemented by using full-text index. A full-text index stores strings with exact meanings in the tabl

implemented in a stored procedure, we use a undocument query hint directly on the statement, which causes the parallel cost threshold of the query to be reduced to 0, which forces the statement to go parallel and the statement execution time from 20 seconds to 5 seconds (note: Using the hash join hint is 7 seconds). The following is a simple example of the effect of using this hint, as shown in Listing 1 of the sample T-sql: from [AdventureWorks]. [S

multi-processor computer. Instead of using an OS thread to execute a query, the job is divided into multiple threads, and complex queries can be completed more quickly and effectively. OptimizationProgramGenerate a query plan and decide when to execute the query in parallel. When making a decision, it considers the following: · Does a computer have multiple processors? · Is the available me