postgresql left join

Inner JOIN (equivalent connection) returns only rows that have the same join field in two tablesLeft join returns records containing all the records in the left table and the equivalent of the junction fields in the right tableRight join returns records that contain all the

In the talk of MySQL before the join grammar or the first review of the coupling of the grammar, oh, in fact, even I have forgotten almost, then we go over it together (if the content has errors or doubt, the domestic information on the MySQL connection is very small, I believe that after reading this article, we will have a fairly clear understanding of the MySQL connection syntax, and will not be confused by the external connection of Oracle ("+").T

First, take a look at some of the simplest examples. Example Table AAid Adate1 A12 A23 A3 TableB Bid Bdate1 B12 B24 B4Two table a,b connected, to remove fields with the same IDSELECT * from a INNER join B on a.aid = B.bid This is the only matching data to be fetched.At this point, the removal is:1 A1 B12 A2 B2 So the left join means:SELECT * from a

Mysql tutorial detailed description of left join SQL left join statementsMysql left join query is a method of joint query. That is to say, two related tables are joined together for query in this way, which makes it easier to call

Preface: Do not sum up and forget it! Let's give a general explanation first. Example Table Aid Adate 1 A1 2 A2 3 A3 Table B Bid Bdate 1 B1 2 B2 4 B4 Problem: two tables A and B are connected and fields with the same ID must be retrieved. Select * from a inner join B on A. Aid = B. Bid this is to retrieve only matching data.

Data Table connection (left join, right join, inner join, Cartesian) -- Query analyzer execution:-- Create Table Table1, Table2:Create Table Table1 (ID int, name varchar (10 ))Create Table Table2 (ID int, score INT)Insert into Table1 select 1, 'lil'Insert into Table1 select 2, 'zhang'Insert into Table1 select

In mysql, we can directly use the left join statement to implement left join. Let's see how to use left join to implement left join for two

Type DefinitionThe inner connection only connects the matched rows.The left Outer Join contains all rows in the left table (no matter whether the table on the right has rows matching them) and all matched rows in the right tableThe right Outer Join contains all rows in the right table (no matter whether the