The difference between join in SQL and the usage of join

1. Join has left Join,right Join,inner join these three kinds, two tables do a Cartesian product, and then select the result set, select the part that satisfies the condition as the result.

• Join (INNER JOIN): Returns a row if there is at least one match in the table (Note: INNER join is the same as join.) ）
• Left JOIN (outer join:): Returns all rows from the left table, even if there is no match in the right table (note: In some databases, the Ieft join is called the OUTER join. ）
• Right join: Returns all rows from the right table, even if there are no matches in the left table (note: In some databases, the correct join is called a OUTER join. ）
• Full join (all outer joins): Returns a row whenever a match exists in one of the tables (note: In some databases, the complete join is called the full OUTER join. ）

2.in is used as a conditional query:

SELECT * from Persons where lastName in (' Adams ', ' Carter ')

Two statements, you can use the SQL optimizer to see how efficiently they perform:

Select COUNT (Distinct (typ.orig_id)) from Sch. Nwstyp Typ left outer join Sch. Nwsatt att on typ.orig_id = att. orig_id where Att.fld_code = ' 4 ' and att.fld_val = ' 1101 ';
Select COUNT (Distinct (typ.orig_id)) from Sch. Nwstyp Typ,sch. Nwsatt att where typ. Typ_code = ' 1501 ' and typ.orig_id = att. orig_id and Att.fld_code = ' 4 ' and att.fld_val = ' 1101 ';

The second SQL above is used by default with the inner join.

The online search also mentions exist.

Found an article:

Http://weblogs.sqlteam.com/mladenp/archive/2007/05/18/60210.aspx

Can see.

The difference between join in SQL and the usage of join