How to add a where clause in a MySQL Insert statement?

Question

This doesn't work:

INSERT INTO users (username, password) VALUES ("Jack","123") WHERE id='1';

Any ideas how to narrow insertion to a particular row by id?

Answer 1

A conditional insert for use typically in a MySQL script would be:

insert into t1(col1,col2,col3,...)
select val1,val2,val3,...
  from dual
 where [conditional predicate];

You need to use dummy table dual.

In this example, only the second insert-statement will actually insert data into the table:

create table t1(col1 int);
insert into t1(col1) select 1 from dual where 1=0;
insert into t1(col1) select 2 from dual where 1=1;
select * from t1;
+------+
| col1 |
+------+
|    2 |
+------+
1 row in set (0.00 sec)

Answer 2

In an insert statement you wouldn't have an existing row to do a where claues on? You are inserting a new row, did you mean to do an update statment?

update users set username='JACK' and password='123' WHERE id='1';