getting data from three different table and inserting it into new table - mysql

Question

I have three tables with contents, now i want to get them and add it into new table but am having this sql error "Column count doesn't match value count at row 1"
here is the sql query.
insert into compare_year(yeara,yearb,yearc,data)
SELECT yeara
FROM table_1
UNION ALL
SELECT yearb, data
FROM table_2
UNION ALL
SELECT yearc
FROM table_3
below is how i created the tables
create table table_1(id int primary key auto_increment,yeara varchar(100));
create table table_2(id int primary key auto_increment,yearb varchar(100),data varchar(100));
create table table_3(id int primary key auto_increment,yearc varchar(100));
my new table is now
create table compare_year(id int primary key auto_increment,yeara varchar(100),yearb varchar(100),yearc varchar(100),data varchar(100))
please can someone help me. thanks

Answer 1

Note:when you union select queries,the number of columns should be equal.
and also you cannot insert mutiple select columns into a single row of another.
My solution will be like:
if three table contain same id,then you can do like this
insert into compare_year(yeara,yearb,yearc,data)
SELECT T1.yeara,T2.yearb,T3.yearc,T2.data
FROM table_1 T1
left Join table_2 T2 on T2.Id = T1.Id
left Join table_3 T3 on T3.Id = T2.Id

Answer 2

It looks like what you want is a JOIN rather than a UNION. When you union two select statements, they must have the same number of fields in the SELECT. For example,
insert into compare_year(yeara)
SELECT yeara
FROM table_1
UNION ALL
SELECT yearb AS yeara
FROM table_2
UNION ALL
SELECT yearc AS yeara
FROM table_3
would be acceptable syntactically. If you want to join the tables,
INSERT INTO compare_year(yeara, yearb, yearc, data)
SELECT table_1.yeara, table_2.yearb, table_3.yearc, table_2.data
FROM table_1, table_2, table_3
but note that this is full cartesian product of the tables. It's likely you want some conditionals as well in a WHERE clause. It's also worth noting that the order of the select cause is what's important for the INSERT, not the field names.