I am currently using the pg_column_size to calculate the size of a row in the DB.
something like:
select pg_column_size(col1, col2, col3..... col10) from _table
Problem is when 1+ column value is null the whole function returns null.
Is there anyway to set a default value for each column within the function to avoid getting null?
try
select pg_column_size(<table_name>.*) from <table_name>;
Are you specifically trying to select a subset of columns?
If you do select pg_column_size(table) from table;, it should work.
Related
I am trying to replace all of the NULL values to 0 in a column of a big table in HIVE.
However, every time I try to implement some code I end up generating a new column to the table. The column I am trying to change/modify still exists and still has the NULL values but the new column that is automatically generated (i.e. _c1) is what I want the column I am trying to modify, to look like.
I tried to run a COALESCE but that also ended up generating a new column. I also tried to implement a CASE WHEN, but the same results ensued.
Select *,
CASE WHEN columnname IS NULL THEN 0
ELSE columnname
END
from tablename;
Also tried
SELECT coalesce(columnname, CAST(0 AS BIGINT)) FROM tablename
I would just like to update the table with the other columns being as is but the column I want to modify still has its original name but instead of NULL values it has 0's that replaced them.
I don't want to generate a new column but modify an existing one.
How should I do that?
Use insert overwrite .. option.
insert overwrite table tablename
select c1,c2,...,coalesce(columnname,0) as columnname
from tablename
Note that you have to specify all the other column names required in select.
I am having a Update Statement on a large volume table.
It updates only one row at a time.
Update MyTable
Set Col1 = Value
where primary key filters
With this update statement gets executed I also want a value in return to avoid a Select Query on a same table to save resources.
What will be my syntax to achieve this?
You can use the RETURNING keyword.
Update MyTable
Set Col1 = Value
where primary key filters
returning column1,column2...
into variable1,variable2...
I have the query:
SELECT MAX(prod_id) FROM products;
It returns the maximum value if there are records. But, if I truncate table and run the same query I am unable to get the max id.
In case you want to query a table's column and suspect that the max function may return null, then you can return 0 in case null is encountered
SELECT NVL(MAX(P.PROD_ID), 0) AS MAX_VAL
FROM PRODUCTS P
This will return at least 0 , if no value is encountered for the column that you mention ()
Yes, by truncating the table you have removed all data in it, with no need for a commit. Therefore there is no data in the table and the max of nothing is nothing.
If you truncate the table, there are no rows left in the table. By definition, Max() returns NULL when run against an empty table.... or did I miss something here?
As Gerald P. Wright commented to an answer, if id is generated by a sequence, you can use it to find the value.
But
SELECT prod_id_seq.currval FROM DUAL
won't work, because currval works only in the session where you fetched a value with currval.
so,
SELECT prod_id_seq.nextval FROM DUAL
can be an workaround for you, but would be a realy, realy BAD solution(if you get the id with this several times you'll get incremented values).
I would like to write a select where I show the value of the field as normal except when the field is null. If it is null I'd like to show a special text, for example "Field is null". How would I best do this?
// Oracle newbie
I like to use function COALESCE for this purpose. It returns the first non-null value from given arguments (so you can test more than one field at a time).
SELECT COALESCE(NULL, 'Special text') FROM DUAL
So this would also work:
SELECT COALESCE(
First_Nullable_Field,
Second_Nullable_Field,
Third_Nullable_Field,
'All fields are NULL'
) FROM YourTable
Just insert the NVL PL/SQL function into your query
SELECT NVL(SOMENULLABLEFIELD,'Field Is Null') SOMENULLABLEFIELD
FROM MYTABLE;
More detail here : http://www.techonthenet.com/oracle/functions/nvl.php
You could also use DECODE:
select value, decode(value, NULL, 'SPECIAL', value) from
(select NULL value from dual
union all
select 2 value from dual
)
I have an Oracle database, and a table with several not null columns, all with default values.
I would like to use one insert statement for any data I want to insert, and don't bother to check if the values inserted are nulls or not.
Is there any way to fall back to default column value when null is inserted?
I have this code:
<?php
if (!empty($values['not_null_column_with_default_value'])) {
$insert = "
INSERT INTO schema.my_table
( pk_column, other_column, not_null_column_with_default_value)
VALUES
(:pk_column,:other_column,:not_null_column_with_default_value)
";
} else {
$insert = "
INSERT INTO schema.my_table
( pk_column, other_column)
VALUES
(:pk_column,:other_column)
";
}
So, I have to omit the column entirely, or I will have the error "trying insert null to not null column".
Of course I have multiple nullable columns, so the code create insert statement is very unreadable, ugly, and I just don't like it that way.
I would like to have one statement, something similar to:
INSERT INTO schema.my_table
( pk_column, other_column, not_null_column_with_default_value)
VALUES
(:pk_column,:other_column, NVL(:not_null_column_with_default_value, DEFAULT) );
That of course is a hypothetical query. Do you know any way I would achieve that goal with Oracle DBMS?
EDIT:
Thank you all for your answers. It seams that there is no "standard" way to achieve what I wanted to, so I accepted the IMO best answer: That I should stop being to smart and stick to just omitting the null values via automatically built statements.
Not exactly what I would like to see, but no better choice.
For those who reading it now:
In Oracle 12c there is new feature: DEFAULT ON NULL. For example:
CREATE TABLE tab1 (
col1 NUMBER DEFAULT 5,
col2 NUMBER DEFAULT ON NULL 7,
description VARCHAR2(30)
);
So when you try to INSERT null in col2, this will automatically be 7.
As explained in this AskTom thread, the DEFAULT keyword will only work as a stand-alone expression in a column insert and won't work when mixed with functions or expressions such as NVL.
In other words this is a valid query:
INSERT INTO schema.my_table
( pk_column, other_column, not_null_column_with_default_value)
VALUES
(:pk_column,:other_column, DEFAULT)
You could use a dynamic query with all rows and either a bind variable or the constant DEFAULT if the variable is null. This could be as simple as replacing the string :not_null_column_with_default_value with the string DEFAULT in your $insert.
You could also query the view ALL_TAB_COLUMNS and use nvl(:your_variable, :column_default). The default value is the column DATA_DEFAULT.
I think the cleanest way is to not mention them in your INSERT-statement. You could start writing triggers to fill default values but that's heavy armor for what you're aiming at.
Isn't it possible to restructure your application code a bit? In PHP, you could construct a clean INSERT-statement without messy if's, e.g. like this:
<?php
$insert['column_name1'] = 'column_value1';
$insert['column_name2'] = 'column_value2';
$insert['column_name3'] = '';
$insert['column_name4'] = 'column_value4';
// remove null values
foreach ($insert as $key => $value) {
if (is_null($value) || $value=="") {
unset($insert[$key]);
}
}
// construct insert statement
$statement = "insert into table (". implode(array_keys($insert), ',') .") values (:". implode(array_keys($insert), ',:') .")";
// call oci_parse
$stid = oci_parse($conn, $statement);
// bind parameters
foreach ($insert as $key => $value) {
oci_bind_by_name($stid, ":".$key, $value);
}
// execute!
oci_execute($stid);
?>
The better option for performance is the first one.
Anyway, as I understand, you don't want to repeat the insert column names and values due the difficult to make modifications. Another option you can use is to run an insert with returning clause followed by an update:
INSERT INTO schema.my_table
( pk_column, other_column, not_null_column_with_default_value)
VALUES
(:pk_column,:other_column, :not_null_column_with_default_value)
RETURNING not_null_column_with_default_value
INTO :insered_value
It seems to work with PHP.
After this you can check for null on insered_value bind variable. If it's null you can run the following update:
UPDATE my_table
SET not_null_column_with_default_value = DEFAULT
WHERE pk_column = :pk_column:
I would like to use one insert
statement for any data I want to
insert, and don't bother to check if
the values inserted are nulls or not.
Define your table with a default value for that column. For example:
create table myTable
(
created_date date default sysdate,
...
)
tablespace...
or alter an existing table:
alter table myTable modify(created_date default sysdate);
Now you (or anyone using myTable) don't have to worry about default values, as it should be. Just know that for this example, the column is still nullable, so someone could explicitly insert a null. If this isn't desired, make the column not null as well.
EDIT: Assuming the above is already done, you can use the DEFAULT keyword in your insert statement. I would avoid triggers for this.