mongodb inner join

bname1 a20050111 1 20060324012 a20050112 2 20060324023 a20050113 3 20060324034 a20050114 4 2006032404Null null 8 2006032408(The number of affected rows is 5) Result description:After careful observation, we will find that the result of left join is exactly the opposite. This time, it is based on the right table (B) and is filled with null when table A is insufficient. 3. Inner joinThe SQL statement is a

of the left table (A) will all be represented, and the right table (B) will only display records that match the search criteria (in the example: A.aid = b.bid).The low-record of table B is null.--------------------------------------------2.right JoinThe SQL statements are as follows:SELECT * FROM ARight Join BOn a.aid = B.bidThe results are as follows:AID Anum BID bname1 a20050111 1 20060324012 a20050112 2 20060324023 a20050113 3 20060324034 a2005011

number of rows affected is 5 rows)Result Description:The left join is based on the records of Table A, a can be regarded as the right table, and B can be regarded as left table.In other words, the records of the left table (A) will all be represented, and the right table (B) will only display records that match the search criteria (in the example: A.aid = b.bid).The low-record of table B is null.--------------------------------------------2.right Joi

only display records for the compound search condition (in the example: A.aid = b.bid). b tables where the records are insufficient are null. Second, right join ... on The MySQL statement is as follows: SELECT * from a right JOIN b on a.aid = B.bid The results are as follows: AID Anum BID Bname 1 a20110111 1 bName0111 2

When a database returns records by connecting two or more tables, an intermediate temporary table is generated, and the temporary table is returned to the user.For example, the following two tables:A (aid int, Aname char (10))B (aid int, Aname char (10))Corresponding data:　　　　　　　　　EXECUTE statement: SELECT * from a left JOIN B on aid=bid　　　　My understanding is that a left connection B, first take a record in a, according to the conditions in the on to

Tags: sql SQ between join Col equivalent connection color none widthDifferences between LEFT JOIN, right join, inner join in SQL　The LEFT join is returned, including　 Records of all records in the left table and the equivalent

Tags: hibernate hql inner join left right Category: SQL Original address: Http://m33707.iteye.com/blog/829725Select from [Outer] The join on the left join returns all rows in "left_table" although there is no matching data in "right_table". Right

TABLE EMPModify ename NOT null; --drop NOT NULL ContraintALTER TABLE EMPModify ENAME null;--drop constraintALTER TABLE EMPDrop constraint unique (name);ALTER TABLE EMPDrop constraint Fk_emp_deptno;--Disabling constraintsALTER TABLE EMPDisable constraint Fk_emp_deptno;--Enable constraintsALTER TABLE EMPEnable constraint Fk_emp_deptno;--oracle connection divided into inner join (

Reproduced in: http://www.2cto.com/database/201206/137067.html Comparison of SQL Server left Join,right join and inner join today to look at the database left join,Right join and INNER

Organize the inner join, left JOIN, right join,Two main tables: dept, EMPOne is the department, one is the employee table structure is as follows:These two tables dept is the primary table EMP is the child table, the associated column is deptnodept performance has dataEMP Performance has dataInner

These two days, in the study of SQL syntax in the use of inner JOIN multi-table query syntax, through learning, found a SQL command, actually involved in a lot of linear algebra knowledge, this knowledge is now systematically recorded as follows:Merging data using relational algebra1 Relational algebraThe theoretical basis for merging data sets is relational algebra, which was proposed by E.f.codd in 1970.I

For example: Table A have 12 (8 + 4) entries, 8 entries have valid relation with BTable B have 80 (77 + 3) entries, 77 entries have valid relation with. Then the return amount of join is:Cross join: 12*80Inner join: 77Full outer join: 77 + 4 + 3Left Outer Join: 77 + 4R

081219 -- Retrieve the public part Select * From t_goods a inner join t_storein BOnA.Gid = B.GID -- All the tables on the right are retrieved, and the tables on the left are matched. Select * From t_goods a right join t_storein BOnA.Gid = B.GID -- Retrieve all tables on the left and matched tables on the right Select * From t_goods a left

Left join returns records that include all records in the left table and join fields in the right table.Right join returns records that include all records in the right table and the joined fields in the left table.Inner join (equivalent join) returns only rows with equal

Table AAid Adate1 A12 A23 A3TableBBid Bdate1 B12 B24 B4Two tables A, B connected, to remove fields with the same IDSELECT * from a INNER join B on a.aid = B.bid This is only the matching data is taken out.At this point, the removal is:1 A1 B12 A2 B2Then the left join means:SELECT * from a LEFT join B on a.aid = B.bidFi

first, data constructionFirst build the table, then talk.Create DatabaseTest UseTestCreate TableA (AIDint Identity(1,1)Primary Key, namenvarchar( -), ageint)Create TableB (BIDint Identity(1,1)Primary Key, namenvarchar( -), Genderint)After creation, insert dataInsertA (Name,age)Values('Zhang San', *)InsertA (Name,age)Values('John Doe', -)InsertA (Name,age)Values('XXX', *)InsertA (Name,age)Values('YYY', *)InsertB (Name,gender)Values('Zhang San',1)InsertB (Name,gender)Values('John Doe',1)InsertB (N

Here's a look at the difference between the inner join, the left JOIN, the right JoinNow I'm assuming there's A and B tables.Left JoinSELECT * from a a left joins b b on a.aid = B.bid;At this point on the left of a table as the base table, a table of data are all displayed, B table of data only shows the display of the conditional expression matching on, the righ

Chat with a friend today and talk about a small problem in their company. As follows: Table A equipment table, storage MAC address, province, city, district.Table B software table, store MAC address, software name.The function is to query the list of software by province, city, or district. What do you think it does now? It obtains the MAC address through the province, the city, or the district, then inquires the B table to use in the query.It is obviously unreasonable to deal with this many-

Tags: style ar sp on c work EF SQL R--preparatory workdrop table if exists Emp;CREATE table if not exists EMP(UID INT primary KEY,Sid int);INSERT into EMP values (+);INSERT into EMP values (2,2);drop table if exists Sal;CREATE table if not exists Sal(Sid Int Primary KEY,Salary float);INSERT into Sal values (1,11);INSERT into Sal values (3,33);--View ResultsSELECT * from EMP LEFT join Sal on emp.sid = Sal.sid;The left table is the main (the left table

The difference between the left join of SQL, right join, INNER joinLeft join returns records that include all the records in the left table and the equivalent of the junction fields in the right tableRight join returns records that include all records in the right table and