How to update table1 with content from table2 with php and mysql

Question

I have two tables in my database, table1 and table2. They are identical. But sometimes I change the data in table1.

How do I copy the data from table1 and update table2 to look the same?

I tried REPLACE INTO table2 SELECT * FROM table1 but it works like INSERT and just make new rows instead of updating the existing ones.

Answer 1

For REPLACE INTO to work as intended, the destination table must have a primary key defined, otherwise MySQL cannot determine whether a row already exists and always assumes a new row. As a result, for tables without a primary key, REPLACE INTO acts exactly like INSERT INTO .

Alternatively, you can use two queries, one UPDATE and one INSERT , with appropriate WHERE (NOT) EXISTS clauses. The advantage of this is that it's portable ( REPLACE INTO is a MySQL extension).

Answer 2

Another alternative is to run two commands...

truncate table table2;
insert into table2 select * from table1;