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  Select top 3 values from each group in a table with SQL

Yesterday, my friend Liu Bing asked me a question about how to select top 3 values for each person in a database table using SQL. I think this question is interesting and it deserves some thoughts. Here I record down how to solve this issue. Assume we have a table which has two columns, one column contains the names of some people and the other column contains some values related to each person. One person can have more than one value. Each value has a numeric type. The question is we want to se...

6,059 0 0          SQL CORRELATED QUERY TOP 3


  Inline IF and CASE statements in MySQL

There are times where running IF statements inside a query can be useful. MySQL provides a simple way to do this through the use of IF and CASE statements. The IF statement takes three arguments; the conditional, the true value and the false value. False and true values may be static values or column values. For example: SELECT IF(score > 100, 100, score) AS score FROM exam_results this will return the value in the score column limited to a maximum value of 100. IF statements can a...

3,190 0 0          SQL CONDITION CASE MYSQK IF


  Removing duplicates in sql

In modern web development, it’s standard practice to make use of a database abstraction layer, typically an Object-Relational Mapper based on either the Active Record pattern or the Data Mapper pattern. There are several pros and cons to this which are fairly well established, so I’ll spare us all from enumerating them all right now. One established pro worth mentioning is that these systems typically provide a high level interface for fetching data, often removing the need to ‘hand wr...

1,858 0 0          SQL WEB DESIGN DUPLICATE REMOVE


  LEFT OUTER JOIN with ON condition or WHERE condition?

The difference is subtle, but it is a big difference. The ON condition stipulates which rows will be returned in the join, while the WHERE condition acts as a filter on the rows that actually were returned.Simple example: Consider a student table, consisting of one row per student, with student id and student name. In a second table, a list of grades that students have received, with student_id, subject, and grade. Give me a list of all students, and show their grade in Math. This requires a LEF...

1,408 0 0          SQL OUTER JO0IN ON WHERE ON VS WHERE WHERE VS ON


  SQL Grammar Summary

整理了一下,希望对大家有用SQL语句大全  --语 句 功 能--数据操作SELECT --从数据库表中检索数据行和列INSERT --向数据库表添加新数据行DELETE --从数据库表中删除数据行UPDATE --更新数据库表中的数据--数据定义CREATE TABLE --创建一个数据库表DROP TABLE --从数据库中删除表ALTER TABLE --修改数据库表结构CREATE VIEW --创建一个视图DROP VIEW --从数据库中删除视图CREATE INDEX --为数据库表创...

2,826 1 0          SQL QUERY SUMMARY SELECT UPDATE DELETE I


  An example of SQL outer join

SELECT MEMBER.Name, MEMBER.Address, ORGANIZER.phoneNo, TRAVEL.Tour_Name, TRAVEL.Start_Date, TRAVEL.End_Date FROM TRAVEL RIGHT JOIN ((MEMBER LEFT JOIN ORGANIZER ON MEMBER.Member_ID=ORGANIZER.memberID) LEFT JOIN PARTICIPATION ON MEMBER.Member_ID=PARTICIPATION.MemberID) ON TRAVEL.TravelID=PARTICIPATION.TravelID;...

1,484 0 0          ACCESS SQL OUTER JOIN