UPDATE table SET column=DEFAULT not working - sqlite

What is the correct way to UPDATE a column to the DEFAULT value?
The documentation suggests that it can be used only in INSERT statements.
drop table if exists testjulian;
create table testjulian(
jul REAL NOT NULL DEFAULT ( julianday('now'))
,whatever STRING);
insert into testJulian values(null,"a"); --null not allowed
insert into testJulian(whatever) values("b"); --default value is used
update testjulian set jul= DEFAULT ; --syntax error
update testjulian set jul= NULL ; --null not allowed

The DEFAULT keyword is limited to being used when creating a table and it is designed for when inserting.
It cannot be used for an update, hence the syntax error.
In your case you could use :-
update testjulian set jul = julianday('now');
Or if you really wanted to dynamically get the DEFAULT value you could extract it from the sql column of sqlite_master.
e.g. using
SELECT sql FROM sqlite_master WHERE name = 'testjulian';
gives you :-
CREATE TABLE testjulian(jul REAL NOT NULL DEFAULT (
julianday('now')),whatever STRING)

Related

Incorrect default value passed to the SQL Server database

I have set my column to int not null default 1... but whenever I save my record, it sets default value for that record to be 0.
I am not setting it anywhere. I don't know where I am making a mistake.
I have debugged my code , and when I am passing new entity object it is setting default value for not null to 0 .May be it is something with LINQ, But I don't know how to handle it.I don't want to explicitly assign value.
Thanks!
For sql-server, you can use SQL Server Profiler to catch all the scripts you run into the DB.
This may show you some details
Try running this query, replacing the 'myTable' and 'myColumn' values with your actual TABLE and COLUMN names, and see what's returned:
SELECT
OBJECT_NAME(C.object_id) AS [Table Name]
,C.Name AS [Column Name]
,DC.Name AS [Constraint Name]
,DC.Type_Desc AS [Constraint Type]
,DC.Definition AS [Default Value]
FROM sys.default_constraints DC
INNER JOIN sys.Columns C
ON DC.parent_column_id = C.column_id
AND DC.parent_object_id = C.object_id
WHERE OBJECT_NAME(DC.parent_object_id) = 'myTable'
AND COL_NAME(DC.parent_object_id,DC.parent_column_id) = 'myColumn'
;
Should return something like this:
[Table Name] [Column Name] [Constraint Name] [Constraint Type] [Default Value]
-------------------------------------------------------------------------------------------
myTable myColumn DF_myTable_myColumn DEFAULT_CONSTRAINT ('0')
If the [Default Value] returned is indeed (1), then it means that you have set the constraint properly and something else is at play here. It might be a trigger, or some other automated DML that you've forgotten/didn't know about, or something else entirely.
I am not the world's biggest fan of using a TRIGGER, but in a case like this, it could be handy. I find that one of the best uses for a TRIGGER is debugging little stuff like this - because it lets you see what values are being passed into a table without having to scroll through mountains of profiler data. You could try something like this (again, switching out the myTable and myColumn values with your actual table and column names):
CREATE TABLE Default_Check
(
Action_Time DATETIME NOT NULL DEFAULT GETDATE()
,Inserted_Value INT
);
CREATE TRIGGER Checking_Default ON myTable
AFTER INSERT, UPDATE
AS
BEGIN
INSERT INTO Default_Check (Inserted_Value)
SELECT I.myColumn
FROM Inserted I
;
END
;
This trigger would simply list the date/time of an update/insert done against your table, as well as the inserted value. After creating this, you could run a single INSERT statement, then check:
SELECT * FROM Default_Check;
If you see one row, only one action (insert/update) was done against the table. If you see two, something you don't expect is happening - you can check to see what. You will also see here when the 0 was inserted/updated.
When you're done, just make sure you DROP the trigger:
DROP TRIGGER Checking_Default;
You'll want to DROP the table, too, once it's become irrelevant:
DROP TABLE Default_Check;
If all of this still didn't help you, let me know.
In VB use
Property VariableName As Integer? = Nothing
And
In C# use
int? value = 0;
if (value == 0)
{
value = null;
}
Please check My Example:
create table emp ( ids int null, [DOJ] datetime NOT null)
ALTER TABLE [dbo].[Emp] ADD CONSTRAINT DF_Emp_DOJ DEFAULT (GETDATE()) FOR [DOJ]
1--Not working for Default Values
insert into emp
select '1',''
2 ---working for Default Values
insert into emp(ids) Values(13)
select * From emp

Setting Default SQLite3 Fields Dynamically

I have an SQLite3 database that I would like to create. I want an INTEGER field (named "Length") to have a DEFAULT value that equals the length of the string in another field (named "Pattern").
CREATE TABLE knowledge (
Entry INTEGER PRIMARY KEY AUTOINCREMENT,
Priority TINYINT UNSIGNED CHECK (0 <= Priority < 15),
Pattern TEXT NOT NULL,
Length INTEGER UNSIGNED DEFAULT 'LENGTH(Pattern);'
);
However, the current table set-up does not "dynamically" set the value of "Length" as desired.
How can I properly set the DEFAULT value of "Length" to be the string length of the "Pattern" field?
The Default value you want to assign is dynamic which sqlite does not support. One solution is what CL. said. I would define the default value as 0 and use not one but two triggers (one for insert and another for update).
CREATE TRIGGER default_length_on_insert AFTER INSERT ON knowledge WHEN NEW.Length IS 0
BEGIN
UPDATE knowledge SET Length=length(NEW.Pattern) WHERE ROWID = NEW.ROWID;
END;
and
CREATE TRIGGER default_length_on_update AFTER UPDATE ON knowledge
BEGIN
UPDATE knowledge SET Length=length(NEW.Pattern) WHERE ROWID = NEW.ROWID;
END;
A default value must be a constant.
You coud use a trigger instead:
CREATE TRIGGER knowledge_length_default
AFTER INSERT ON knowledge
FOR EACH ROW
WHEN NEW.Length IS NULL
BEGIN
UPDATE knowledge
SET Length = length(NEW.Pattern)
WHERE Entry = NEW.Entry;
END;

setting default value while creating table in SQLite

I am working on SQLite. I want to create a table namely user_role with two column role_id and role_name. And there is an another table namely default that contain role_name and default_val.
I want to set Default value of role_id in the time of creating the table user_role and the Default value have to be retrieved from the table default.
I am new to SQLite and have to idea about the way to doing such recursive query. Please help.
The documentation says:
An explicit DEFAULT clause may specify that the default value is NULL, a string constant, a blob constant, a signed-number, or any constant expression enclosed in parentheses.
You would need to use a subquery, which is not allowed.
However, you could use a trigger that sets the ID if none was specified:
CREATE TRIGGER user_role_id_default
AFTER INSERT ON user_role
FOR EACH ROW
WHEN NEW.role_id IS NULL
BEGIN
UPDATE user_role
SET role_id = (SELECT default_val
FROM "default"
WHERE role_name = NEW.role_name)
WHERE rowid = NEW.rowid;
END;

Modify a column to NULL - Oracle

I have a table named CUSTOMER, with few columns. One of them is Customer_ID.
Initially Customer_ID column WILL NOT accept NULL values.
I've made some changes from code level, so that Customer_ID column will accept NULL values by default.
Now my requirement is that, I need to again make this column to accept NULL values.
For this I've added executing the below query:
ALTER TABLE Customer MODIFY Customer_ID nvarchar2(20) NULL
I'm getting the following error:
ORA-01451 error, the column already allows null entries so
therefore cannot be modified
This is because already I've made the Customer_ID column to accept NULL values.
Is there a way to check if the column will accept NULL values before executing the above query...??
You can use the column NULLABLE in USER_TAB_COLUMNS. This tells you whether the column allows nulls using a binary Y/N flag.
If you wanted to put this in a script you could do something like:
declare
l_null user_tab_columns.nullable%type;
begin
select nullable into l_null
from user_tab_columns
where table_name = 'CUSTOMER'
and column_name = 'CUSTOMER_ID';
if l_null = 'N' then
execute immediate 'ALTER TABLE Customer
MODIFY (Customer_ID nvarchar2(20) NULL)';
end if;
end;
It's best not to use dynamic SQL in order to alter tables. Do it manually and be sure to double check everything first.
Or you can just ignore the error:
declare
already_null exception;
pragma exception_init (already_null , -01451);
begin
execute immediate 'alter table <TABLE> modify(<COLUMN> null)';
exception when already_null then null;
end;
/
You might encounter this error when you have previously provided a DEFAULT ON NULL value for the NOT NULL column.
If this is the case, to make the column nullable, you must also reset its default value to NULL when you modify its nullability constraint.
eg:
DEFINE table_name = your_table_name_here
DEFINE column_name = your_column_name_here;
ALTER TABLE &table_name
MODIFY (
&column_name
DEFAULT NULL
NULL
);
I did something like this, it worked fine.
Try to execute query, if any error occurs, catch SQLException.
try {
stmt.execute("ALTER TABLE Customer MODIFY Customer_ID nvarchar2(20) NULL");
} catch (SQLException sqe) {
Logger("Column to be modified to NULL is already NULL : " + sqe);
}
Is this correct way of doing?
To modify the constraints of an existing table
for example... add not null constraint to a column.
Then follow the given steps:
1) Select the table in which you want to modify changes.
2) Click on Actions.. ---> select column ----> add.
3) Now give the column name, datatype, size, etc. and click ok.
4) You will see that the column is added to the table.
5) Now click on Edit button lying on the left side of Actions button.
6) Then you will get various table modifying options.
7) Select the column from the list.
8) Select the particular column in which you want to give not null.
9) Select Cannot be null from column properties.
10) That's it.

How to handle a missing feature of SQLite : disable triggers?

How to handle a missing feature of SQLite: disable triggers?
I don't have it stored the name of triggers for a specific table.
For example how can I drop all triggers?
What would you do?
So here it is 2015 and there still is no 'disable triggers' in SQLite. For a mobile Application this can be problematic--especially if it's a corporate App requiring offline functionality and local data.
An initial data load can be slowed to crawl by trigger execution even when you don't wrap each insert in an individual transaction.
I solved this issue using SQLite SQL fairly simply. I have a settings table that doesn't participate in the init load. It holds 'list' of key/value pairs. I have one key called 'fireTrigger' with a bit value of 0 or 1. Every trigger I have has an expression that selects value and if it equals 1 it fires the trigger, otherwise it doesn't.
This expression is in addition to any expressions evaluated on the data relating to the trigger. e.g.:
AND 1 = (SELECT val FROM MTSSettings WHERE key = 'fireTrigger')
In simple clean effect this allows me to disable/enable the trigger with a simple UPDATE to the settings table
I wrote a very simple extension function to set a boolean value to true or false.
And a function to retrieve this value (GetAllTriggersOn()).
With this function I can define all my triggers like:
CREATE TRIGGER tr_table1_update AFTER UPDATE ON TABLE1 WHEN GetAllTriggersOn()
BEGIN
-- ...
END
SQLite stores schema (meta) information in the built-in sqlite_master table.
To get a list of available triggers use the below query:
SELECT name FROM sqlite_master
WHERE type = 'trigger' -- AND tbl_name = 'a_table_name'
Set a flag in your database and use it in the triggers WHEN condition.
Say you want to create a trigger on the "clients" table after an insert. You have created a table "trigger_settings" with a TINYINT "triggers_on" field - this is your flag. Then you can set the field to 0 if you want to turn off the filters and to 1 when you want to turn them back on.
Then you create your filter with a WHEN condition that checks the "triggers_on" field.
For example:
CREATE TRIGGER IF NOT EXISTS log_client_data_after_insert
AFTER INSERT
ON [clients]
WHEN (SELECT triggers_on FROM trigger_settings)=1
BEGIN
your_statement
END;
Maybe you can make a stored procedures for droping and creating them. Is that good for you ?
Expanding on Nick Dandoulakis's answer, you could drop all relevant triggers and then reinstate them before the transaction's completion:
BEGIN;
SELECT name, sql FROM sqlite_master WHERE type = 'trigger' AND tbl_name = 'mytable';
-- store all results
-- for each name: DROP TRIGGER $name;
-- do normal work
-- for each sql: execute the SQL verbatim
COMMIT;
Expanding other answers this is how i'm doing it. Take into account that this is disabling all triggers for all tables in the database except some of then used by spatialite
SQLITE_FILE=/tmp/my.sqlite
# Define output sql files as variables
CREATE_TRIGGER_SQL=/tmp/create_triggers.sql
DROP_TRIGGER_SQL=/tmp/drop_triggers.sql
## Dump CREATE TRIGGER statements to a file ##
# To wrap statements in a transaction
echo -e "BEGIN;\n\n" > "${CREATE_TRIGGER_SQL}"
# `SELECT sql` does not output semicolons, so we must concatenate them
sqlite3 -bail "${SQLITE_FILE}" "SELECT sql || ';' FROM sqlite_master WHERE type = 'trigger' AND (name NOT LIKE 'gid_%' AND name NOT LIKE 'ggi_%' AND name NOT LIKE 'ggu_%' AND name NOT LIKE 'gii_%' AND name NOT LIKE 'giu_%' AND name NOT LIKE 'vwgcau_%' AND name NOT LIKE 'vtgcau_%' AND name NOT LIKE 'gcau_%' AND name NOT LIKE 'geometry_columns_%' AND name NOT LIKE 'gcfi_%' AND name NOT LIKE 'gctm_%' AND name NOT LIKE 'vtgcfi_%' AND name NOT LIKE 'vwgcfi_%' AND name NOT LIKE 'vtgcs_%' AND name NOT LIKE 'vwgc_%' AND name NOT LIKE 'vtgc_%' AND name NOT LIKE 'gcs_%');" >> "${CREATE_TRIGGER_SQL}"
echo -e "\n\nCOMMIT;" >> "${CREATE_TRIGGER_SQL}"
## Dump DROP TRIGGER statements to a file ##
echo -e "BEGIN;\n\n" > "${DROP_TRIGGER_SQL}"
sqlite3 -bail "${SQLITE_FILE}" "SELECT 'DROP TRIGGER ' || name || ';' FROM sqlite_master WHERE type = 'trigger' AND (name NOT LIKE 'gid_%' AND name NOT LIKE 'ggi_%' AND name NOT LIKE 'ggu_%' AND name NOT LIKE 'gii_%' AND name NOT LIKE 'giu_%' AND name NOT LIKE 'vwgcau_%' AND name NOT LIKE 'vtgcau_%' AND name NOT LIKE 'gcau_%' AND name NOT LIKE 'geometry_columns_%' AND name NOT LIKE 'gcfi_%' AND name NOT LIKE 'gctm_%' AND name NOT LIKE 'vtgcfi_%' AND name NOT LIKE 'vwgcfi_%' AND name NOT LIKE 'vtgcs_%' AND name NOT LIKE 'vwgc_%' AND name NOT LIKE 'vtgc_%' AND name NOT LIKE 'gcs_%');" >> "${DROP_TRIGGER_SQL}"
echo -e "\n\nCOMMIT;" >> "${DROP_TRIGGER_SQL}"
## Execute like ##
sqlite3 -bail /"${SQLITE_FILE}" < "${DROP_TRIGGER_SQL}"
# do things
sqlite3 -bail /"${SQLITE_FILE}" < "${CREATE_TRIGGER_SQL}"

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