Is it a good practice to store column name to represent what were the changes made in a data in parent table which led to trigger the audit.
Ex :-
create table employee
(
emp_id character varying(10),
fname character varying(30),
lname character varying(30),
tel_no character varying(15)
);
create table aud_employee
(
emp_id character varying(10),
fname character varying(30),
lname character varying(30),
tel_no character varying(15)
aud_col_changed character varying(100)
);
--
insert into employee values('215','Mark','Cooper','222-458-254');
This will also result to insert the record in an audit table through trigger and will have null value in aud_col_changed column.
Now when I update the same record :-
update employee set tel_no='255-458-254' where emp_id='215';
So, audit would also be created for this update made and audit table should now consist another record and would consist value 'tel_no' in aud_col_changed column.
If there are multiple columns changed at a time, it would be separated by comma in same field.
If this is the right approach, could you please describe the ways of achieving it?
Please note that the table on which I am trying to implement this approach has around 18 columns out of whih 6-7 columns are JSON.
Your method is likely to be fine -- you should specify what you want to do with the audit table.
Personally, I would rather have a table where the audit table was one of the following:
One row per column changed, with the old value and the new value.
One row per row changed, with all the columns appearing twice, once for the old value and once for the new value.
In other words, I usually want to see both the old and new values together.
The first method is tricky when dealing with columns that have different types. The second is tricky when you want to modify the structure of the table.
I did some more research and I found that if we want to store column name then that data needs to be updated through function. In function we need to check each value passed with NOT NULL. If it appears to be not null then we need to hard code the column name and assign it to the variable. If more values are found which are NOT NULL, then that hard coded column name needs to be appended to main variable until we check all the values passed in function with NOT NULL.
This will definitely degrade performance of DB and making it run after every update is obviously not preferable.
Hence, I will not prefer using audit_col_changed column.
Related
I want to add another row in my existing table and I'm a bit hesitant if I'm doing the right thing because it might skew the database. I have my script below and would like to hear your thoughts about it.
I want to add another row for 'Jane' in the table, which will be 'SKATING" in the ACT column.
Table: [Emp_table].[ACT].[LIST_EMP]
My script is:
INSERT INTO [Emp_table].[ACT].[LIST_EMP]
([ENTITY],[TYPE],[EMP_COD],[DATE],[LINE_NO],[ACT],[NAME])
VALUES
('REG','EMP','45233','2016-06-20 00:00:00:00','2','SKATING','JANE')
Will this do the trick?
Your statement looks ok. If the database has a problem with it (for example, due to a foreign key constraint violation), it will reject the statement.
If any of the fields in your table are numeric (and not varchar or char), just remove the quotes around the corresponding field. For example, if emp_cod and line_no are int, insert the following values instead:
('REG','EMP',45233,'2016-06-20 00:00:00:00',2,'SKATING','JANE')
Inserting records into a database has always been the most common reason why I've lost a lot of my hairs on my head!
SQL is great when it comes to SELECT or even UPDATEs but when it comes to INSERTs it's like someone from another planet came into the SQL standards commitee and managed to get their way of doing it implemented into the final SQL standard!
If your table does not have an automatic primary key that automatically gets generated on every insert, then you have to code it yourself to manage avoiding duplicates.
Start by writing a normal SELECT to see if the record(s) you're going to add don't already exist. But as Robert implied, your table may not have a primary key because it looks like a LOG table to me. So insert away!
If it does require to have a unique record everytime, then I strongly suggest you create a primary key for the table, either an auto generated one or a combination of your existing columns.
Assuming the first five combined columns make a unique key, this select will determine if your data you're inserting does not already exist...
SELECT COUNT(*) AS FoundRec FROM [Emp_table].[ACT].[LIST_EMP]
WHERE [ENTITY] = wsEntity AND [TYPE] = wsType AND [EMP_COD] = wsEmpCod AND [DATE] = wsDate AND [LINE_NO] = wsLineno
The wsXXX declarations, you will have to replace them with direct values or have them DECLAREd earlier in your script.
If you ran this alone and recieved a value of 1 or more, then the data exists already in your table, at least those 5 first columns. A true duplicate test will require you to test EVERY column in your table, but it should give you an idea.
In the INSERT, to do it all as one statement, you can do this ...
INSERT INTO [Emp_table].[ACT].[LIST_EMP]
([ENTITY],[TYPE],[EMP_COD],[DATE],[LINE_NO],[ACT],[NAME])
VALUES
('REG','EMP','45233','2016-06-20 00:00:00:00','2','SKATING','JANE')
WHERE (SELECT COUNT(*) AS FoundRec FROM [Emp_table].[ACT].[LIST_EMP]
WHERE [ENTITY] = wsEntity AND [TYPE] = wsType AND
[EMP_COD] = wsEmpCod AND [DATE] = wsDate AND
[LINE_NO] = wsLineno) = 0
Just replace the wsXXX variables with the values you want to insert.
I hope that made sense.
I've created a table schema and specified that for some attributes, values cannot be null. For one column of this table, values are to be imported from a column of some another table but the problem i am facing is that when i use insert statement to copy values from that column of another table to the column of this newly created table, the attributes of this new column start screaming because they kind of have a constraint on them that while insertion their values cannot be NULL!
How do i cope with this?
One solution is that for other attributes, just for time being, i can state that null values can be accommodated so that i can successfully import values from column of other table and then later on put condition on the remaining attributes that values are not be NULL. But how do i do do this?
You need to convert NULL to some DEFAULT values while importing.
I am not sure which DB engine you are using, in mysql:
Use something like IFNULL(column_name, "").
Reference
You may simply be looking for the default clause. When you define a column, you can specify;
intcol int not null default 0
If the column is not specified for an insert, then it will default to 0. In some databases, if a NULL value is supplied, it will also get the default value.
I am working in SQL Server 2008. I have a table with many columns that will not have values (at least, for the given situation). So, they will have a NULL value when I query each of them. I would like to instead make these NULL values be empty strings (i.e., ''). What is the best way to achieve this? My current idea is to set a DEFAULT value of '' on each them at the time that the table is created. However, since there are so many of them, this will be very tedious.
You have 2 options:
As you said, give it a default value of empty string for columns you don't want to be null when you create table/add new columns.
When you select nullable columns from the table you can use IsNull(ColumnName,'') which means if ColumnName is null it'll return empty string ('').
Create a table with the same structure as your current table, with a different name, and the default value as ''.
Insert into that table from your original table.
Delete the original table.
Change the name of the new table to the original table name.
I am trying to export my Database as an .dbf by using a VBA script, but the dbf requires the database to have certain values for the column size.
When I leave the columns as they are in Access, I get an error saying
field will not fit in record
How can I set the column size for each column seperatly? Preferably while generating the table, so I don't have to do it manually everytime i generate a new table with queries
And where do I set them? (in a Query or in SQL?)
Thanks in advance!
Edit:
I have made sure that its the field size value that is giving me the error. I changed all the field size values manually by opening the table in Design View.
So now the second part of my question is becoming more crucial. Wether or not it is possible to set the field size while generating the table.
Edit2:
I am currently using SQL in a query to create the table as followed:
SELECT * INTO DB_Total
FROM Tags_AI_DB;
After the initial DB_Total is made, I use several Insert into queries to add other rows:
INSERT INTO DB_TOTAL
SELECT a.*
FROM Tags_STS_ENA_DB AS a
LEFT JOIN DB_TOTAL AS b
ON a.NAME = b.NAME
WHERE b.NAME IS NULL;
If I set the column values in the DB_Total table while generating it with the Select into query, will they still have those values after using the Insert Into queries to insert more rows?
Edit3:
I decided (after a few of your suggestions and some pointers from colleagues, that it would be better to first make my table and afterwards update this table with queries.
However, it seems like I have run into a dead end with Access, this is the code I am using:
CREATE TABLE DB_Total ("NAME" char(79),"TYPE" char(16), "UNIT" char(31),
"ADDR" char(254), "RAW_ZERO" char(11), "RAW_FULL" char(11), "ENG_ZERO" char(11),
"ENG_FULL" char(11), "ENG_UNIT" char(8), "FORMAT" char(11), "COMMENT" char(254),
"EDITCODE" char(8), "LINKED" char(1), "OID" char(10), "REF1" char(11), "REF2" char(11),
"DEADBAND" char(11), "CUSTOM" char(128), "TAGGENLINK" char(32), "CLUSTER" char(16),
"EQUIP" char(254), "ITEM" char(63), "HISTORIAN" char(6),
"CUSTOM1" char(254), "CUSTOM2" char(254), "CUSTOM3" char(254), "CUSTOM4" char(254),
"CUSTOM5" char(254), "CUSTOM6" char(254), "CUSTOM7" char(254), "CUSTOM8" char(254))
These are all the columns required for me to make a DBF file that is accepted by the application we are using it with.
You'll understand my sadness when this generated the following error:
Record is too large
Is there anything I can do to make this table work?
UPDATE
The maximum record size for Access 2007 is around 2kB (someone will no doubt correct that value)
When you create CHAR(255) it will use 255 bytes of space regardless as to what is in the field.
By contrast, VARCHARs do not use up space (only enough to define them) until you put something in the field, they grow dynamically.
Changing the CHAR(x)s to VARCHAR(x)s you will shrink the length of your table to within permitted values. Be aware that you may come into trouble if the row you are trying to insert is larger than the 2kB limit.
Previous
The way to specify column lengths when generating the table is to use a CREATE TABLE statement instead of a SELECT * INTO.
CREATE TABLE DB_Total
(
Column1Name NVARCHAR(255) --Use whatever datatype and length you need
,Column2Name NUMERIC(18,0) --Use whatever datatype and length you need
,...
) ;
INSERT INTO DB_Total
....
If you use a SELECT * INTO statement, SQL will use whatever field lengths and types it finds in the existing data.
It is also better practice to list the column names in your insert statement, so instead of
INSERT INTO DB_TOTAL
SELECT a.*
You should put:
INSERT INTO DB_Total
(
Column1Name
,Column2Name
,...
)
SELECT a.Column1Name
,a.Column2Name
,...
FROM ...
WHERE ... ;
In Edit2, you indicated your process starts with a "make table" (SELECT INTO) query which creates DB_Total and loads it with data from Tags_AI_DB. Then you run a series of "append" (INSERT) queries to add data from other tables.
Now your problem is that you need specific field size settings for DB_Total, but it is impossible to define those sizes with a "make table" query.
I think you should create DB_Total one time and set the field sizes as you wish. Do that manually with the table in Design View, or execute a CREATE TABLE statement if you prefer.
Then forget about the "make table" query and use only "append" queries to add the data.
If the issue is that this is a recurring operation and you want to discard previous data before importing the new, execute DELETE FROM DB_Total instead of DROP TABLE DB_Total. That will allow you to preserve the structure of the (now empty) DB_Total table so you needn't fiddle with setting the field sizes again.
Seems to me the only potential issue then might be if the structure of the source tables changes. If that happens, revise the structure of DB_Total so that it's compatible again.
I have a table with a column which contains a 'valid until' Date and I want to make sure that this can only be set to null in a single row within the table. Is there an easy way to do this?
My table looks like this (postgres):
CREATE TABLE 123.myTable(
some_id integer NOT NULL,
valid_from timestamp without time zone NOT NULL DEFAULT now(),
valid_until timestamp without time zone,
someString character varying)
some_id and valid_from is my PK. I want nobody to enter a line with a null value in column valid_until if there is already a line with null for this PK.
Thank you
In PostgreSQL, you have two basic approaches.
Use 'infinity' instead of null. Then your unique constraint works as expected. Or if you cannot do that:
CREATE UNIQUE INDEX null_valid_from ON mytable(someid) where valid_until IS NULL
I have used both approaches. I find usually the first approach is cleaner and it allows you to use range types and exclude constraints in newer versions of PostgreSQL better (to ensure no two time ranges overlap based on a given given someid), bt the second approach often is useful where the first cannot be done.
Depending on the database, you can't have null in a primary key (I don't know about all databases, but in sql server you can't). The easiest way around this I can think of is to set the date time to the minimum value, and then add a unique constraint on it, or set it to be the primary key.
I suppose another way would be to set up a trigger to check the other values in the table to see if another entry is null, and if there is one, don't allow the insert.
As Kevin said in his answer, you can set up a database trigger to stop someone from inserting more than one row where the valid until date is NULL.
The SQL statement that checks for this condition is:
SELECT COUNT(*)
FROM TABLE
WHERE valid until IS NULL;
If the count is not equal to 1, then your table has a problem.
The process that adds a row to this table has to perform the following:
Find the row where the valid until value is NULL
Update the valid until value to the current date, or some other meaningful date
Insert the new row with the valid until value set to NULL
I'm assuming you are Storing Effective-dated-records and are also using a valid from date.
If so, You could use CRUD stored procedures to enforce this compliance. E.G the insert closes off any null valid dates before inserting a new record with a null valid date.
You probably need other stored procedure validation to avoid overlapping records and to allow deleting and editing records. It may be more efficient (in terms of where clauses / faster queries) to use a date far in the future rather than using null.
I know only Oracle in sufficient detail, but the same might work in other databases:
create another column which always contains a fixed value (say '0') include this column in your unique key.
Don't use NULL but a specific very high or low value. I many cases this is actually easier to use then a NULL value
Make a function based unique key on a function converting the date including the null value to some other value (e.g. a string representation for dates and 'x' for null)
make a materialized view which gets updated on every change on your main table and put a constraint on that view.
select count(*) cnt from table where valid_until is NULL
might work as the select statement. And a check constraint limiting the cnt value to the values 0 and 1
I would suggest inserting to that table through an SP and putting your constraint in there, as triggers are quite hidden and will likely be forgotten about. If that's not an option, the following trigger will work:
CREATE TABLE dbo.TESTTRIGGER
(
YourDate Date NULL
)
CREATE TRIGGER DupNullDates
ON dbo.TESTTRIGGER
FOR INSERT, UPDATE
AS
DECLARE #nullCount int
SELECT #nullCount = (SELECT COUNT(*) FROM TESTTRIGGER WHERE YourDate IS NULL)
IF(#NullCount > 1)
BEGIN
RAISERROR('Cannot have Multiple Nulls', 16, 1)
ROLLBACK TRAN
END
GO
Well if you use MS SQL you can just add a unique Index on that column. That will allow only one NULL. I guess that if you use other RDBMS, this will still function.