complex sql queries tutorial

Tags: color col Left connection pre strong select complex IV efficiencyA, b two tables, find the ID field, there is a table, but there is no data in table B. A total of 13w data, after the deduplication of about 3W data, b table has 2W data, and B table ID field is indexed. Method One Easy to understand with not in, low efficiency ~ Execution Time: 1.395 seconds ~ Select distinct from where not inch (Select from B) Method Two Use left Join...on ...,

SQL queries all database names, table names, stored procedures, and parameter lists 1. Get all user names: Select name from sysusers where status = '2' and islogin = '1' Islogin = '1' indicates the account Islogin = '0' indicates the role Status = '2' indicates the user account Status = '0' indicates a unified account. 2. Get all database names: Select name from Ma

statement when your query is relatively simple, every time you create a SQL statement from scratch is not time-consuming, however, complex queries are different, each time from scratch will produce a lot of development errors. So, once you have SQL running smoothly, you'd better save them and call them when you need th

#方法一: Use not in, easy to understand, low efficiency ~ Execution Time: 1.395 seconds ~Select COUNT (1) from Ecs_goods WHERE ecs_goods.goods_id not in (SELECT ecs_member_price.goods_id from Ecs_member_price);#方法二: Use left Join...on ..., "b.id isnull" indicates a record of NULL in the b.ID field after the connection is connected-execution time: 0.739 seconds ~SELECT COUNT (1) from ecs_goods left JOIN ecs_member_price on ecs_goods.goods_id=ecs_member_price.goods_id WHERE Ecs_ MEMBER_PRICE.GOODS_ID

: Database Maintenance Plan MS SQL Basics Tutorial: System Database MS SQL Basics Tutorial: Instance database MS SQL Basics Tutorial: Creating Database Tables MS SQL Basics

the computer. Configure the SQL Server max server memory server configuration option to 1.5 times times the physical memory (half of the virtual memory size setting).7) Increase the number of server CPUs, but it is important to understand that parallel processing of serial processing requires resources such as memory. The use of parallel or string travel is the MSSQL automatic evaluation option. A single task is decomposed into multiple tasks and can

');8. Query for empty/non-empty statements of field contentsSql>select * from emp WHERE Mgr Is/is not NULL;9. Using Logical operation SymbolsSql>select * from emp WHERE (sal>500 or job= ' MANAGE ') and ename like ' j% ';10. Sort the results of the query by the values of the fieldsSql>select * from emp ORDER by Deptno, Sal DESC; (by department ascending, and by salary descending)Second, complex query1. Data Grouping (Max,min,avg,sum,count)

High concurrency Database design Dimension model: Star, snowflake model Standardization Data volume Big, easy to tens Small, generally not more than millions SQL Read-write scenario Regular import, no updates, complex queries retrieve large amounts of data every time Read and write s

for writing the data to the network cache and sending it to the client. The results returned from execution are not cached anywhere, but are returned to the client as soon as they are generated. Obviously, returning data over the network to the client is constrained by the network traffic Control Protocol. If the client fails to take the returned data in time, it eventually blocks the sending behavior of the data sender and causes the query execution to be suspended. When the data reception abi

universal table Expression (CTEs) is a new feature of SQL Server 2005. They are similar to the alias (as in the Select t1.* from MyTable T1), but are more powerful. In essence, a CTE is a temporary result set that exists only in the statement in which it occurs. You can create a CTE in the Select, INSERT, DELETE, update, or cteate view statements. A CTE is similar to a derived table, but has several advantages. The advantages of a CTE Unlike derived

, as shown in the code is like this, lazy classmate can directly ctrl+c/ctrl+v:select Table1. Name, Table1. Time, Table1. Training content, Table2. Name from Table1,table2 WHERE Table1. Name = Table2. NameThe basic meaning is to filter the records in table 1 and the names in table 2 from table 1. The SELECT statement is one of the most basic and most important statements in the SQL language, and with the constraints after the where statement, most of

-outer JOIN displays all rows in the right table SELECT * FROM T1 right outer join T3 on T1.userid=t3.userid Run Result: UserID username password userid JF DJ 1 Jack Jackpwd 1 20 3 NULL NULL NULL 3 50 6 IV: FULL OUTER JOIN displays all rows in both tables SELECT * FROM T1 full outer join T3 on T1.userid=t3.userid Run Result: UserID username password userid JF DJ 1 Jack Jackpwd 1 20 3 2 Owen OWENPWD null NULL NULL NULL NULL NULL 3 50 6 Summary, on the joint inquiry, I have already tested. The eff

PHP's YII framework uses database configuration and SQL Operations Examples tutorial, yii example Tutorial Database access (DAO)YII contains a data access layer (DAO) built on top of the PHP PDO. DAO provides a unified set of APIs for different databases. Where ActiveRecord provides interaction between the database and the model (M,model in MVC), QueryBuilder is

Label:In most cases, programmers prefer to use in to query for data that meets certain criteria, and the in statement has recently been used in a method that queries which users have a role: SELECT COUNT(1) fromBaseuserWHEREBaseuser.deletionstatecode= 0 andBaseuser.enabled= 1 andBaseuser.isvisible= 1 andBaseuser.id> 0 andBaseuser.idinch(SELECTUserId fromSpysxtuserroleWHERERoleid= '6d989d918dfe428c95e4469f866b1299' and

Searching the Internet for cross-server queries, presumably linked server (pre-storage connection mode and ensure connectivity) and OpenDataSource (written in the statement, the portability of strong). Depending on the function used, the performance difference is obvious ... Although very simple, but LZ was pit for a few days only to find, ashamed.1. Linked ServerVery useful function, add the method if there is a problem can contact LZ alone, not very

T3 on T1.userid=t3.useridRun Result: UserID username password userid JF DJ1 Jack Jackpwd 1 20 3NULL NULL NULL 3 50 6IV: FULL OUTER JOIN displays all rows in both tablesSELECT * FROM T1 full outer join T3 on T1.userid=t3.useridRun Result: UserID username password userid JF DJ1 Jack Jackpwd 1 20 32 Owen OWENPWD null NULL NULLNULL NULL NULL 3 50 6Summary, on the joint inquiry, I have already tested. The efficiency is indeed relatively high, 4 kinds of Union way if can use flexibly, basically

Tutorial on Database Configuration and SQL operations in the PHP Yii framework, and tutorial on yii instances Database Access (DAO)Yii contains a data access layer (DAO) built on php pdo ). DAO provides a unified set of APIS for different databases. activeRecord provides interaction between databases and models (M, Model in MVC). QueryBuilder is used to create dy

. Graduater_business.gradbusinessid = dbo. Graduater_graduaterregist.graduaterguid INNER JOIN dbo. Person_contact ON dbo. Person_basicinfo.personid = dbo. Person_contact.personid INNER JOIN dbo. Person_skill ON dbo. Person_basicinfo.personid = dbo. Person_skill.personid INNER JOIN dbo. Person_employpurpose ON dbo. Person_basicinfo.personid = dbo. Person_employpurpose.personid OPTION (FORCE order) ( With the above steps, we can already implement automatic optimization o

Website construction tutorial (7): SQL Elementary tutorial tip: SQL is a standard computer language for accessing and processing databases. SQL is a standard computer language used to access and process databases. Use SQL to mana

The following articles mainly introduce the basic tutorial of SQL coding optimization for the IBM DB2 database. The importance of such a specific query is that the more important the query is, you may need to optimize indexes by creating indexes. If you are coding the query that the CIO is running every day, make sure it provides the best performance. Therefore, it is important to create an index for this s