Sql – PostgreSQL: insert from another table


I'm trying to insert data to a table from another table and the tables have only one column in common. The problem is, that the TABLE1 has columns that won't accept null values so I can't leave them empty and I can't get them from the TABLE2.

I have TABLE1:
id, col_1 (not null), col_2(not null), col_3 (not null)

and TABLE2:
id, col_a, col_b, col_c

so how could I insert id from TABLE2 to TABLE1 and fill the col_1-3 with hard coded strings like "data1", "data2", "data3"?

INSERT INTO TABLE1 (id) SELECT id FROM TABLE2 WHERE col_a = "something";

will result in:

ERROR: null value in column "col_1" violates not-null constraint

Best Solution

You can supply literal values in the SELECT:

INSERT INTO TABLE1 (id, col_1, col_2, col_3)
SELECT id, 'data1', 'data2', 'data3'
WHERE col_a = 'something';

A select list can contain any value expression:

But the expressions in the select list do not have to reference any columns in the table expression of the FROM clause; they can be constant arithmetic expressions, for instance.

And a string literal is certainly a value expression.