mysql join multiple tables

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 development of our business requirements are sometimes complex,

Mysql-join query, mysql-joinThree methods of MySQL association query: SELECT * FROM film JOIN film_actor ON (film. film_id = film_actor.film_id );SELECT * FROM film JOIN film_actor USING (film_id); -- when the field names of the

1. Why duplicate data appears when two tables are connected2. What is the connection process of the table?Example:Table A:10Table B:1002EXECUTE statement: SELECT * from A join B on a.id = b.id;The order is as follows:Tables formed by join:1 11 01 01 20 10 00 00 2On after:1 10 00 0Therefore, duplicate data appears after the table is connected　　　　There is a one-to-

The following articles mainly describe the usage of MySQL left join, right join, and inner join) detailed analysis of the following articles is mainly to explain the actual operations in the form of an instance demonstration, the following is the detailed description of the article. The following is an example Table

. 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 join: Retu

The following is a test example.1. Create two temporary tables and input test data:Copy codeThe Code is as follows:Create table # temptest1(Id int,Name1 varchar (50 ),Age int)Create table # temptest2(Id int,Name1 varchar (50 ),Age int) The following table data is queried: # Temptest1 # temptest2 2. Now we need to update the age in # temptest2 to the corresponding age in # temptest1. In fact, the age of ID 1 in [Table 1] is changed to 19, and the ag

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 join D By C.Id =D.CId Whe

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

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,