Rename column only if exists

Better to have two functions, one calling the other:

CREATE OR REPLACE FUNCTION column_exists(ptable TEXT, pcolumn TEXT)
  RETURNS BOOLEAN AS $BODY$
DECLARE result bool;
BEGIN
    -- Does the requested column exist?
    SELECT COUNT(*) INTO result
    FROM information_schema.columns
    WHERE
      table_name = ptable and
      column_name = pcolumn;
    RETURN result;
END$BODY$
  LANGUAGE plpgsql VOLATILE;

CREATE OR REPLACE FUNCTION rename_column_if_exists(ptable TEXT, pcolumn TEXT, new_name TEXT)
  RETURNS VOID AS $BODY$
BEGIN
    -- Rename the column if it exists.
    IF column_exists(ptable, pcolumn) THEN
        EXECUTE FORMAT('ALTER TABLE %I RENAME COLUMN %I TO %I;',
            ptable, pcolumn, new_name);
    END IF;
END$BODY$
  LANGUAGE plpgsql VOLATILE;

Please read this article on codingvila.com for a detailed explanation.

DO $$
BEGIN
  IF EXISTS(SELECT *
    FROM information_schema.columns
    WHERE table_name='your_table' and column_name='your_column')
  THEN
      ALTER TABLE "public"."your_table" RENAME COLUMN "your_column" TO "your_new_column";
  END IF;
END $$;

@NessBird 2 function approach is good but the Column_Exists function can be reduced to a select exists, avoiding counting, and as an SQL function instead of a plpgsql function.

create or replace function 
column_exists(ptable text, pcolumn text, pschema text default 'public')
  returns boolean 
  language sql stable strict  
as $body$
    -- does the requested table.column exist in schema?
    select exists 
         ( select null 
             from information_schema.columns 
             where table_name=ptable 
               and column_name=pcolumn 
               and table_schema=pschema
         ); 
$body$;

I added the schema parameter to handle multiple schema with the same table name. The rename_column_if_exists remains unchanged except for the possible addition of schema.

You can simply handle the error that may be raised in an anonymous code block:

DO
$$
    BEGIN
        ALTER TABLE t
            RENAME COLUMN c1 TO c2;
    EXCEPTION
        WHEN undefined_column THEN RAISE NOTICE 'column t.c1 does not exist';
    END;
$$;

You can omit the text after THEN to do nothing:

DO
$$
    BEGIN
        ALTER TABLE t
            RENAME COLUMN c1 TO c2;
    EXCEPTION
        WHEN undefined_column THEN
     END;
$$;

You will probably only be getting a number when the error happens. You can find the condition name (the error name after the WHEN) from here. Make sure you are on the right version for your database.