Bi-sql - different join

Different JOIN

White tea has been described before JOIN Some basic usage of , But actually JOIN There are several types of variants .

Different JOIN, The result returned is also different .

JOIN There are several types of ：

JOIN, If there is at least one match in the table , Then go back to the line ;

LEFT JOIN, Even if there is no match in the right table , Also return all rows from the left table ;

RIGHT JOIN, Even if there is no match in the left table , Also returns all rows from the right table ;

FULL JOIN, As long as there is a match in one of the tables , Just go back .

Basic grammar

grammar ：

SELECT  Column name (*) FROM  surface 1 name  (JoinType) JOIN  surface 2 name  ON  surface 1 name .[ Column fields ] =  surface 2 name .[ Column fields ]

Be careful

INNER It can be omitted by default ,JOIN Equate to INNER JOIN.

Using examples

Case data ：

In the database of white tea machine , There is a name “TEST” The database of , There is a name “Customer” The dimension table and the name are “Fact” The fact sheet of , Two tables go through IDKEY relation .

Example 1：

JOIN usage . stay PowerBI Use in JOIN take Customer Table and Fact Table for association query .

SELECT Customer.[NAME],Fact.[AMOUNT] FROM Customer JOIN Fact ON Customer.[IDKEY]=Fact.[IDKEY]

give the result as follows ：

The result returned at this point , Whether it's Customer Watch or Fact No matching items in the table will appear .

Example 2：

LEFT JOIN usage . stay PowerBI Use in LEFT JOIN take Customer Table and Fact Table for association query .

SELECT Customer.[NAME],Fact.[AMOUNT] FROM Customer LEFT JOIN Fact ON Customer.[IDKEY]=Fact.[IDKEY]

give the result as follows ：

The result returned at this point , Take the left table Customer Table based , Whether the matching item is in Fact Is there... In the table , All items in the left table will be rendered .

Example 3：

RIGHT JOIN usage . stay PowerBI Use in RIGHT JOIN take Customer Table and Fact Table for association query .

SELECT Customer.[NAME],Fact.[AMOUNT] FROM Customer RIGHT JOIN Fact ON Customer.[IDKEY]=Fact.[IDKEY]

give the result as follows ：

The result returned at this point , To the right Fact Table based , Whether the matching item is in Customer Is there... In the table , All items in the right table will be rendered .

Example 4：

FULL JOIN usage . stay PowerBI Use in FULL JOIN take Customer Table and Fact Table for association query .

SELECT Customer.[NAME],Fact.[AMOUNT] FROM Customer FULL JOIN Fact ON Customer.[IDKEY]=Fact.[IDKEY]

give the result as follows ：

The result returned at this point , Mainly double tables , Whether the corresponding item exists in other tables or not , Will present .

JOIN Different types of , The result returned is also different , The specific usage depends on our actual application scenarios and business logic , Start according to your needs .

This is white tea , One PowerBI Beginners .