What is the difference between SQL statements
create temp table temp_1 And
create table #temp_1
used in creating temporary table or are both the same ?
Figured it out, both syntax does the same work !!
Users can either use the temp keyword or a # sign right before the table name to create a temporary table (Redshift Temp Table). In other words, to create a Redshift Temp Table, simply specify the TEMPORARY keyword (or TEMP abbreviation) or # sign in your CREATE TABLE DDL statement.
syntax 1 : CREATE TABLE #table_name (column_name1 data_type1,column_name2 data_typ2);
Syntax 2: CREATE TEMPORARY TABLE table_name (column_name1 data_type1,column_name2 data_typ2);
Syntax 3: CREATE TEMP TABLE table_name (column_name1 data_type1,column_name2 data_typ2);
Supporting documents on same -->
https://docs.aws.amazon.com/redshift/latest/dg/r_CREATE_TABLE_NEW.html
https://hevodata.com/learn/redshift-temp-tables/#c2
Related
I have a large system, and table schema updates quite offtenly, I noticed that after times of removing and recreating new cloumn, limitation "tables can have at most 1600 columns" is shown, but still there are few columns in information_schema.columns.
I've tried vacuum full analyze, still not working, any way to avoid this limitation?
DO $$
declare tbname varchar(1024);
BEGIN
FOR i IN 1..1599 LOOP
tbname := 'alter table vacuum_test add column test' || CAST(i AS varchar(8)) ||' int';
EXECUTE tbname;
END LOOP;
END $$;
alter table vacuum_test drop column test1;
VACUUM FULL ANALYZE vacuum_test;
alter table vacuum_test add column test1 int;
result:
alter table vacuum_test add column test1 int
> ERROR: tables can have at most 1600 columns
> 时间: 0.054s
Unfortunately vacuum full does not remove dropped columns from the table (i.e. entries that have attisdropped = true in `pg_attribute). I would have expected that, but apparently this does not happen.
The only way to get rid of the hidden columns is to create a brand new table and copy the data to the new table.
Something along the lines:
create table new_table (like old_table including all);
insert into new_table
select *
from old_table;
Then drop the old table and rename the new one to the old name. Constraint and index names will be named differently, so you might want to rename them as well.
You will have the re-create all foreign keys (incoming and outgoing) manually as they are not included when using CREATE TABLE (LIKE ...).
Another option is to use pg_repack which does this transparently in the background without locking the table.
I'm trying to change all the USER-DEFINED columns to TEXT in a specific view using pgsql.
Is it possible to do that in a single alter table query ou do I need to check first what columns contain that dataype and then perform the dataype change one by one?
This is what I'm trying:
ALTER TABLE if exists "schemaName"."Table_A"
ALTER COLUMN (
select column_name
from information_schema.columns inf
where table_name = 'Table_A' and inf.data_type = 'USER-DEFINED')
TYPE TEXT;
I'm getting and error in the subquery start "("
You need to do this one by one. Generally speaking such DDL statements cannot work on several objects in one statement.
For ALTER TABLE, see: https://www.postgresql.org/docs/12/sql-altertable.html.
FOR ALTER VIEW, see: https://www.postgresql.org/docs/current/sql-alterview.html
I'm coming from a background in SQL Server where I would create temp tables using the:
select id
into #test
from table A
I've just moved into a PostGresql environment and I was hoping I could do the same, but I'm getting a syntax error. I did a search and it seems like you have to do a Create Table statement.
Is it not possible to easily create temp tables in Postgres?
Postgres supports SELECT INTO, so this should work fine:
SELECT id
INTO TEMP TABLE test
FROM a
You can also use CREATE TABLE AS:
CREATE TEMP TABLE test AS
SELECT id FROM a
This version is generally preferred, as the CREATE statement provides additional options, and can also be used in PL/pgSQL functions (where the SELECT INTO syntax has been hijacked for variable assignment).
I am working with hive version 0.9 and I need delete columns of a hive table. I have searched in several manuals of hive commands but I only I have found commands to version 0.14. Is possible to delete a column of a hive table in hive version 0.9? What is the command?
Thanks.
We can’t simply drop a table column from a hive table using the below statement like sql.
ALTER TABLE tbl_name drop column column_name ---- it will not work.
So there is a shortcut to drop columns from a hive table.
Let’s say we have a hive table.
From this table I want to drop the column Dob. You can use the ALTER TABLE REPLACE statement to drop a column.
ALTER TABLE test_tbl REPLACE COLUMNS(ID STRING,NAME STRING,AGE STRING); you have to give the column names which you want to keep in the table
There isn't a drop column or delete column in Hive.
A SELECT statement can take regex-based column specification in Hive releases prior to 0.13.0, or in 0.13.0 and later releases if the configuration property hive.support.quoted.identifiers is set to none.
That being said you could create a new table or view using the following:
drop table if exists database.table_name;
create table if not exists database.table_name as
select `(column_to_remove_1|...|column_to_remove_N)?+.+`
from database.some_table
where
...
;
This will create a table that has all the columns from some_table except the columns named column_to_remove_1, ... , to column_to_remove_N. You can also choose to create a view instead.
ALTER TABLE table_name REPLACE COLUMNS ( c1 int, c2 String);
NOTE: eliminate column from column list. It will keep matched columns and removed unmentioned columns from table schema.
we can not delete column from hive table . But droping a table(if its external) in hive and the recreating table(with column excluded) ,wont delete ur data .
so what can u do is(if u dont have table structure) run this command :
show create table database_name.table_name;
Then you can copy it and edit it (with column eliminated).Afterwards you can do as per invoke the shell
table details are empid,name,dept,salary ,address. i want remove address column. Just write REPLACE COLUMNS like below query
jdbc:hive2://> alter table employee replace columns(empid int, name string,dept string,salary int);
As mentioned before, you can't drop table using an alter statement.
Alter - replace is not guaranteed to work in all the cases.
I found the best answer for this here:
https://stackoverflow.com/a/48921280/4385453
For example, there is a table named 'testtable' that has following columns: testint (integer) and testtext (varchar(30)).
What i want to do is pretty much something like that:
INSERT INTO testtable VALUES(15, CONTENT_OF_FILE('file'));
While reading postgresql documentation, all I could find is COPY TO/FROM command, but that one's applied to tables, not single columns.
So, what shall I do?
If this SQL code is executed dynamically from your programming language, use the means of that language to read the file, and execute a plain INSERT statement.
However, if this SQL code is meant to be executed via the psql command line tool, you can use the following construct:
\set content `cat file`
INSERT INTO testtable VALUES(15, :'content');
Note that this syntax is specific to psql and makes use of the cat shell command.
It is explained in detail in the PostgreSQL manual:
psql / SQL Interpolation
psql / Meta-Commands
If I understand your question correctly, you could read the single string(s) into a temp table and use that for insert:
DROP SCHEMA str CASCADE;
CREATE SCHEMA str;
SET search_path='str';
CREATE TABLE strings
( string_id INTEGER PRIMARY KEY
, the_string varchar
);
CREATE TEMP TABLE string_only
( the_string varchar
);
COPY string_only(the_string)
FROM '/tmp/string'
;
INSERT INTO strings(string_id,the_string)
SELECT 5, t.the_string
FROM string_only t
;
SELECT * FROM strings;
Result:
NOTICE: drop cascades to table str.strings
DROP SCHEMA
CREATE SCHEMA
SET
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "strings_pkey" for table "strings"
CREATE TABLE
CREATE TABLE
COPY 1
INSERT 0 1
string_id | the_string
-----------+---------------------
5 | this is the content
(1 row)
Please note that the file is "seen" by the server as the server sees the filesystem. The "current directory" from that point of view is probably $PG_DATA, but you should assume nothing, and specify the complete pathname, which should be reacheable and readable by the server. That is why I used '/tmp', which is unsafe (but an excellent rendez-vous point ;-)