Sql: insert subquery result to column

Question

I have a table with several columns. I want to create a new column from an existing one. Say column "A" is text, I want to insert into column "B" the left 10 characters of column "A".

I do:

insert into table (B) select left(A, 10) from table;

However, I want this to be aligned with column "A" not as new rows, how do I do that?

Sergey Kalinichenko · Accepted Answer · 2018-02-10 17:09:04Z

2

I want this to be aligned with column "A" not as new rows

Insert adds new rows. Since you need to update existing ones, use UPDATE:

UPDATE MyTable
SET B = LEFT(A, 10)

edited Feb 10, 2018 at 17:09

answered Feb 10, 2018 at 17:02

Sergey Kalinichenko

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3 Comments

user Over a year ago

That was so simple. Thank you!

Lukasz Szozda Over a year ago

ERROR: cannot use column references in default expression + I don't think that PostgreSQL supports computed/generated columns yet.

Sergey Kalinichenko Over a year ago

@lad2025 Right, Postgres doesn't allow it. Thank you!

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