Insert Data into Table C from Table A in MySQL

For this, use left join on table A and B. Let us create the first table −

mysql> create table demo20
−> (
−> id int,
−> name varchar(20)
−> );
Query OK, 0 rows affected (1.87 sec)

Insert some records into the table with the help of insert command −

mysql> insert into demo20 values(100,'John');
Query OK, 1 row affected (0.07 sec)

mysql> insert into demo20 values(101,'Bob');
Query OK, 1 row affected (0.24 sec)

mysql> insert into demo20 values(102,'Mike');
Query OK, 1 row affected (0.12 sec)

mysql> insert into demo20 values(103,'Carol');
Query OK, 1 row affected (0.15 sec)

Display records from the table using select statement −

mysql− select *from demo20;

This will produce the following output −

+------+-------+
|  id | name   |
+------+-------+
|  100 | John  |
|  101 | Bob   |
|  102 | Mike  |
|  103 | Carol |
+------+-------+
4 rows in set (0.00 sec)

Following is the query to create second table −

mysql> create table demo21
−> (
−> id int,
−> name varchar(20)
−> );
Query OK, 0 rows affected (1.70 sec)

Insert some records into the table with the help of insert command −

mysql> insert into demo21 values(100,'Sam');
Query OK, 1 row affected (0.12 sec)

mysql> insert into demo21 values(101,'Adam');
Query OK, 1 row affected (0.14 sec)

mysql> insert into demo21 values(133,'Bob');
Query OK, 1 row affected (0.13 sec)

mysql> insert into demo21 values(145,'David');
Query OK, 1 row affected (0.15 sec)

Display records from the table using select statement −

mysql> select *from demo21;

This will produce the following output −

+------+-------+
| id   | name  |
+------+-------+
|  100 | Sam   |
|  101 | Adam  |
|  133 | Bob   |
|  145 | David |
+------+-------+
4 rows in set (0.00 sec)

Following is the query to create third table −

mysql> create table demo22
−> (
−> id int,
−> name varchar(20)
−> );
Query OK, 0 rows affected (1.39 sec)

Now, let’s say, demo20 has table name A, demo21 has B and demo22 has C. The query is as follows to insert data into table C if data is not in table B comparing to A −

mysql> insert into demo22(id,name)
−> select tbl1.id,tbl1.name from demo20 tbl1
−> left join demo21 tbl2 on tbl2.id=tbl1.id
−> where tbl2.id is null;
Query OK, 2 rows affected (0.21 sec)
Records: 2 Duplicates: 0 Warnings: 0

Display records from the table using select statement −

mysql> select *from demo22;

This will produce the following output −

+------+-------+
| id   | name  |
+------+-------+
|  102 | Mike  |
|  103 | Carol |
+------+-------+
2 rows in set (0.00 sec)