identical rows

Hiya Aggro

Forgive my ignorance, but like I say, I'm a beginner at this stuff, but
could you explain:

select
table1.id as table1_id,
table2.id as table2_id
from table1,table2

i.e. I'm a little puzzed by the "table1.id as table1_id" (the last bit)

Is table1.id the primary key of table1? What is table1_id?

Geoff

"Aggro" wrote in message

 > Geoff Jones wrote:
 >
  >> Suppose I have two tables. How can I find if the two have "identical
  >> rows"; in the sense that they are allowed to have different primary keys
  >> but in respect to all the other fields they are the same.
 >
 > You need to join those two tables and search rows where all wanted columns
 > have similar values. Something like this:
 >
 > select
 > table1.id as table1_id,
 > table2.id as table2_id
 > from table1,table2
 > where
 > table1.column1 = table2.column1 and
 > table1.column2 = table2.column2 and
 > table1.column3 = table2.column3;
 >
 > Be aware that this can return the same id values multiple times if you got
 > multiple duplicates.
 >> Stay informed about: identical rows 

Geoff Jones wrote:

 > i.e. I'm a little puzzed by the "table1.id as table1_id" (the last bit)
 >
 > Is table1.id the primary key of table1? What is table1_id?

table1_id is just a alias for the id in table1. And the example assumed
that you have a table named table1 and table2 and both have column named
id as their primary key. Without the alias, your query would return just
two columns, both named as "id", so it would be harder for you to know
which id belongs to which table.

The name of alias is not much ruled, so you could say:
select
table1.id as cat,
table2.id as dog

And it would be as valid and working. But I like naming the aliases so
that you know the table and column from the name.
 >> Stay informed about: identical rows 

Thanks Aggro

"Aggro" wrote in message

 > Geoff Jones wrote:
 >
  >> i.e. I'm a little puzzed by the "table1.id as table1_id" (the last bit)
  >>
  >> Is table1.id the primary key of table1? What is table1_id?
 >
 > table1_id is just a alias for the id in table1. And the example assumed
 > that you have a table named table1 and table2 and both have column named
 > id as their primary key. Without the alias, your query would return just
 > two columns, both named as "id", so it would be harder for you to know
 > which id belongs to which table.
 >
 > The name of alias is not much ruled, so you could say:
 > select
 > table1.id as cat,
 > table2.id as dog
 >
 > And it would be as valid and working. But I like naming the aliases so
 > that you know the table and column from the name.
 >> Stay informed about: identical rows