I would like to add a generated column to a very large table without locking it:
alter table customer alter column foo text generated always as ((infos_json->'customerinfos'->>'redirect')) stored;
Is there a way to do this without locking? Maybe concurrently?
Is there a way to add a column alias to an existing table, which just references another existing column in the table? such that reads and writes to the new column name will go to the existing column name. Sort of how a view in postgres can act as a read / write alias:
create view temp_order_contacts as (select * from order_emails)
This will make read / write possible to order_emails table but by calling temp_order_contacts instead.
Is there something similar but for columns?
Assuming this is for backwards compatibility; you want to rename a column, but you also want to existing queries to still work.
You can rename the table and create a view with the original name.
-- Move the existing table out of the way.
alter table some_table rename to _some_table;
-- Create a view in its place.
create view some_table as (
select
*,
-- provide a column alias
some_column as some_other_column
from _some_table
);
I am trying to create a temporary table in postgres by copying the column names and types from an existing table.
CREATE TEMPORARY TABLE temporary_table LIKE grades;
Typing the query into Postgre, it tells me about an error in LIKE. Is "Like" keyword not usable in Postgre or am I doing something wrong?
You need to wrap the like statement in parentheses:
CREATE TEMPORARY TABLE temporary_table (LIKE grades);
If you want defaults or indexes included as well, you need to add that explicitly
CREATE TEMPORARY TABLE temporary_table
(LIKE grades INCLUDING INDEXES INCLUDING DEFAULTS);
Is there any way to create a postgis table with existing style from layer_styles table? Say for example i have so many styles stored in layer_styles table. I need to assign one of the style from layer_styles table to the new table which i am going to create. Can that be done using postgresql during table creation using sql command?
You need to identify the layer IDs of interest (or name, or any column you want) and to create the new table using this data+structure. However using the style in this secondary table may not be that easy
create table public.layer_styles_2 as
(select * from public.layer_styles where id in (2,3));
Is there a way to set the PRIMARY KEY in a single "CREATE TABLE AS" statement?
Example - I would like the following to be written in 1 statement rather than 2:
CREATE TABLE "new_table_name" AS SELECT a.uniquekey, a.some_value + b.some_value FROM "table_a" AS a, "table_b" AS b WHERE a.uniquekey=b.uniquekey;
ALTER TABLE "new_table_name" ADD PRIMARY KEY (uniquekey);
Is there a better way of doing this in general (assume there are more than 2 tables, e.g. 10)?
According to the manual: create table and create table as you can either:
create table with primary key first, and use select into later
create table as first, and use add primary key later
But not both create table as with primary key - what you wanted.
If you want to create a new table with the same table structure of another table, you can do this in one statement (both creating a new table and setting the primary key) like this:
CREATE TABLE mytable_clone (
LIKE mytable
INCLUDING defaults
INCLUDING constraints
INCLUDING indexes
);
No, there is no shorter way to create the table and the primary key.
See the command below, it will create a new table with all the constraints and with no data. Worked in postgres 9.5
CREATE TABLE IF NOT EXISTS <ClonedTableName>(like <OriginalTableName> including all)
well in mysql ,both is possible in one command
the command is
create table new_tbl (PRIMARY KEY(`id`)) as select * from old_tbl;
where id is column with primary key of old_tbl
done...
You may do this way
CREATE TABLE IOT (EMPID,ID,Name, CONSTRAINT PK PRIMARY KEY( ID,EMPID))
ORGANIZATION INDEX NOLOGGING COMPRESS 1 PARALLEL 4
AS SELECT 1 as empid,2 id,'XYZ' Name FROM dual;