如何从mysql表中选择唯一记录

Question

I have two tables

table1

id|col1|col2|col3 

table2 

id|colA|colB|colC

both table has is as primary key

col1 in table1 is unique and would not allow duplicate value. I am trying to migrate the data from table2 to table1. The columns are mapped in the following manner

table1.id => table2.id
table1.col1 => table2.colA
table1.col2 => table2.colB
table1.col3 => table2.colC

I Used the following query to migrate the data

inert into table1 select id,colA,colB,colC from table2

Mysql complain about colA having duplicate value. Then I use

insert into table1 select id,distinct(colA),colB,colC from table2 

Mysql complain about bad syntax. Could you please help me writing the correct query to migrate data from table2 to table1.

Thanks

Answer 1

Actually, you can lose some data, while saving in this way. Because If colB and colC are different for the same colA, only one of the rows will be saved.

You can use this query:

INSERT INTO table1 
    SELECT id,colA,colB,colC 
    FROM table2
    GROUP BY colA;