mongodb inner join

Original Data SheetVideo Information Sheet Tab_video_infoPlay record table Tab_play_recordDemandCount the top 20 videos that have been played (have already been played); select a.video_id, sum (' Is_play ') Span style= "COLOR: #0000ff" >as total from ' tab_video_info ' as a inner join ' Tab_play_record ' as b on a.video_id = b.video_id group by a.video_id order by total desc limit 0 ,

INNER JOIN ... The syntax format of on can be summarized as:From ((Table 1 INNER join table 2 on table 1. Field number = Table 2. Field number) INNER join table 3 on table 1. Field number = Table 3. Field number)

SQL join usage (full, left, out, inner) A. Cross join Cartesian product if there is no where Condition Clause, it will return the Cartesian product of the two joined tables, and the number of rows returned is equal to the product of the number of rows of the two tables;For example, the execution results of A, B, and C are the same but the effic

Label:Summary : In this tutorial, you'll learn how to use the MySQL INNER JOIN clause to select data from multiple table s based on join conditions.Introducing MySQL INNER JOIN clauseThe MySQL INNER

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Inner joins, also known as natural joins, only two tables match the rows to appear in the result set. The returned result set selects all matching data from two tables, discarding unmatched data. Because an inner join removes all rows from the result table that do not match the other connection tables, the internal connection may cause information loss. The

Label:Purpose of inner join on in sql: (equivalent connection)SELECT * FROM A inner join B on a.no=b.no; A record of all numbers equal to B is queried, which is equivalent to: SELECT * from A a, where a.no=b.no; Multi-Table query: SELECT * FROM (table 1 inner

1. Connection statements used in the WHERE clause are called implicit connections in the database language. Inner join ...... The connection generated by the on clause is called an explicit connection. (Other join parameters are also explicit connections.) There is no essential difference between the connection relationship between where and

Refer from:http://explainextended.com/2009/07/16/inner-join-vs-cross-apply/INNER JOINUsed construct in SQL: It joins and together, selecting only those row combinations for which A JOIN condition is true.This query:SELECT *from table1join table2on table2.b = table1.aReads For each row from table1 ,

Take a look at the following two statements:SELECT * FROM table1 inner JOIN table2 on table1.id = table2.idSELECT * from table1,table2 where table1.id = Table2.idIn fact, the results of the implementation of the two methods are the same, the specific difference is as follows:The connection statement used in the 1.WHERE clause, in the database language, is called the implicit connection.

1. The connection statement used in the WHERE clause, in the database language, is called an implicit connection. INNER JOIN ... An ON clause produces a connection called a dominant connection. (Other join parameters are also dominant connections) the connection between the WHERE and the inner