I am trying to replicate a functionality from SQL Server into redshift where I have to ignore column if the column exists, otherwise add it into the table.
I have come across these posts, however couldn't find a proper solution from them:
I am able to get a TRUE
or FALSE
for columns that I want to check. But I don't know how to ALTER
the table to add or remove one.
These are some of my attempts:
IF (SELECT EXISTS(SELECT * FROM pg_catalog.pg_table_def
WHERE schemaname = 'my_schema'
AND tablename = 'my_table'
AND "column" = 'my_new_column'
)) <> TRUE
THEN
ALTER TABLE my_table
ADD COLUMN my_new_column varchar
END IF;
CREATE OR REPLACE PROCEDURE if_else()
LANGUAGE plpgsql
AS $$
BEGIN
IF (SELECT EXISTS(SELECT * FROM pg_catalog.pg_table_def
WHERE schemaname = 'my_schema'
AND tablename = 'my_table'
AND "column" = 'my_new_column'
)) <> TRUE
THEN
ALTER TABLE my_table
ADD COLUMN my_new_column varchar
END IF;
END;
$$
;
CALL if_else();
A few more failed attempts:
CREATE OR REPLACE PROCEDURE alter_my_table()
AS $$
BEGIN
ALTER TABLE my_table
ADD COLUMN my_new_column varchar
END;
$$
LANGUAGE plpgsql
;
SELECT
CASE WHEN COUNT(*) THEN 'warning: column exists already.'
ELSE CALL alter_my_table();
END
FROM pg_catalog.pg_table_def
WHERE schemaname = 'my_schema'
AND tablename = 'my_table'
AND "column" = 'my_new_column'
Thank you for your time.
I have done something like this, which works fairly well.
CREATE OR REPLACE PROCEDURE add_table_column(s_name varchar, t_name varchar, c_name varchar, c_type varchar)
LANGUAGE plpgsql
AS $$
BEGIN
IF (SELECT count(1) FROM pg_catalog.pg_table_def
WHERE schemaname = s_name
AND tablename = t_name
AND "column" = c_name
) = 0
THEN
execute 'ALTER TABLE '||s_name||'.'||t_name||' ADD COLUMN '||c_name||' '||c_type;
END IF;
END;
$$
;
create table public.tst (col1 numeric);
call add_table_column('public','tst','col2','numeric');
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