sql join 2 tables

Nner Join joins two tables, three tables, five tables of SQL statements2013-04-14 15:13: 11来 Source: West e-Net SQL INNER join keyword indicates that the INNER

1. What is joinJoin: Join indicates the relationship between two tables. we can regard two tables as two sets. Suppose there are two tables, which are represented by a and B. The two tables have one or more identical fields. There are three different sets:1. Intersection: re

SQL statement Optimization-query different rows of the two tables NOT IN, NOT EXISTS, Join query Left Join, existsleft In actual development, we often need to compare the differences between two or more tables and compare the data that is the same and the data is different.

(1) Cross join is what we call the Cartesian product. Query the number of records that satisfy both tables, A (3 Records), B (9 Records), A*b (27 records).For example: An employee table (hr.employees) and a freight company (sales.shippers) table make a cross-connection.1 SELECT * FROM hr.employees;2 select * from Sales.shippers;After the cross-connect, 27 recor

Tags: Connection Method field name comparison field record right outer connection outer JOIN mode use 1-- inner connection: INNER JOIN It represents a matching record that returns two tables or Recordset join fields, representing the portions of the two tables that are cont

records that this action occurs in the PGA's work area, so it does not consume logical reading;3. The hash connection applies only to the CBO, and it can only be used for equivalent connection conditions (even if the hash is an inverse connection, Oracle actually converts it to an equivalent equivalent connection);4. Hash joins are well suited for table joins between a small table ( result set ) and a large table, especially if the connection column of a small table is very selective, the execu

Label:Here are two tables TableA and TableB, the name table and the age table, for the test data for our example TableA Id Name 1 T1 2 T2 4 T4 TableB Id Age 1 18 2 20 3 19 In the de

finally found on Wikipedia as an argument.SQL defines two different syntax ways to represent "connections." The first is the explicit join symbol, which uses the keyword explicitly, followed by JOIN the implicit join symbol, which uses the so-called implicit join symbol. The implicit

. Method Three: Using connection query Connection queries include: 1. Self-connect (join equals inner JOIN): Query result is data that exists on both sides 2. Left join to the left join: return all data on the right, return to the back, null not present 3. Right

put this probe data aside. By the way, the value of this probe will be placed in memory first, if later accumulated a certain amount of other probe on the data, Oracle will write these data in bulk to disk, this is the graph of dump probe partitions to disk.3. After we have scanned the probe intact, we may have returned some of the matching data, but we now have two pieces of data that are not processed on the disk: part of the hash table of the build table and part of the data for probe table,

SQL statements (a couple of tables together to query, get the first few to the more than 10 data): 1. If there are a,b,c,d four tables, a,b,c,d are linked together as follows: The ((A Inner join B By A.Id =B.AId) Inner join C By B.Id =C.BId)Inner

The use of ExistsSelect *from haha where exists (select *from bumen where Bumen.code = haha.bumen and bumen.name = ' Sales department ') and AGE>35(Run method is query-by-clause)Select Name,sex,age, (select name from bumen where Bumen.code = haha.bumen) as department from hahaSelect Name,sex,age, (select name from bumen where Bumen.code = haha.bumen) as department, (select CEO from bumen where Bumen.code = Haha.bumen) as CEO from hahaA simple way to connect two

Table:Person+-------------+---------+| Column Name | Type |+-------------+---------+| PersonId | int | | FirstName | varchar | | LastName | varchar |+-------------+---------+personid is the primary key, column for this table.Table:Address+-------------+---------+| Column Name | Type |+-------------+---------+| Addressid | int | | PersonId | int | | City | varchar | | State | varchar |+-------------+---------+addressid are the primary key column for thi

sides2. Left join to the left join: return all data on the right, return to the back, null not present3. Right join: Return all data on the right, return on left, no null4. Fully connected full join: Returns if one of the tables exists and the other does not exist as Nul

Recently, the company is recruiting people. My colleagues asked a few questions about database connection that I think the database can be applied ~Now I want to write about their functions here.Assume that the following table is used:One is the voting master table, and the other is the voter information table ~ Record the IP address of the voter and the corresponding voting type. The left-right connection is actually the result of our joint query. Which table prevails ~1: For example, right

((Member INNER join Membersort on Member.membersort=membersort.membersort) INNER join Me Mberlevel on Member.memberlevel=memberlevel.memberlevel) INNER JOIN memberidentity on member.memberidentity= The memberidentity.memberidentity syntax format can be summarized as: from (table 1 INNER JOIN table

Assume that the following table is used: One is the voting master table, and the other is the voter information table ~ Record the IP address of the voter and the corresponding voting type. The left-right connection is actually the result of our joint query. Which table prevails ~1: for example, right join or right outer join:Take the voter table on the right as the standard. The record in the left table (votemaster) is displayed only when its ID

a row in the left table, a null value is returned for the left table.(2) SQL statementsSelect * From Table1 right join Table2 on table1.id = table2.id------------- Result -------------Idnameidscore------------------------------1lee1902zhang2100Nullnull370------------------------------Note: all the clauses containing Table 2