postgresql INSERT INTO with IF statement

Question

In postgresql , how to INSERT values in a column.b from column.a from same table Where

IF column.a = 1 then column.b = foo, 
IF column.a = 2 then column.b = bar,
IF column.a = 3 then column.b = good,
IF column.a = 4 then column.b = bad

Answer 1

INSERT does not insert values into columns. It inserts new rows into your table. Instead, you need to use an UPDATE statement . You will also need some ifs inside .

Answer 2

If the row already exists, you do not need an INSERT . You need an UPDATE like this:

UPDATE your_table
SET b = CASE 
        WHEN a = 1 then 'foo'
        WHEN a = 2 then 'bar'
        WHEN a = 3 then 'good'
        ELSE 'bad'
        END
WHERE some_condition = 'true';