I want to write sql script that should check if column exists in the table, and then remove the column if previous statement is true. The database I use is Sybase ASE, and this is the code that I tried to use:
IF EXISTS (SELECT 1 FROM syscolumns WHERE id = object_id('users') AND name = 'maiden_name')
BEGIN
ALTER TABLE security DROP maiden_name
END
The code above executed successfully first time I run it. The second time I goth the error:
Invalid column name 'maiden_name'
If column does not exist the ALTER TABLE block of code shouldn't run. Is there a way to achieve this is Sybase? Thank you.
You can use dynamic SQL:
IF EXISTS (SELECT 1 FROM syscolumns WHERE id = object_id('users') AND name = 'maiden_name')
BEGIN
EXEC('ALTER TABLE security DROP maiden_name')
END;
The problem is that the parser is trying to parse the ALTER during the compilation phase, and it gets an error if the column does not exist.
Related
As part of the company I am working for at the moment I need to create some database upgrade scripts to replace some work of a previous contractor.
The code before the following block runs, creates the new ID column, and then this script looks to populate the values and then drop some columns.
IF EXISTS (
SELECT *
FROM sys.columns
WHERE object_id = OBJECT_ID(N'[Central].[Core.Report].[ReportLessonComp]')
AND name = 'Name')
and
EXISTS (
SELECT *
FROM sys.columns
WHERE object_id = OBJECT_ID(N'[Central].[Core.Report].[ReportLessonComp]')
AND name = 'Code')
BEGIN
UPDATE
[Central].[Core.Report].[ReportLessonComp]
SET
CompetencyId = rc.Id
FROM
[Central].[Core.Report].[ReportLessonComp] rlc
INNER JOIN
[Core.Lookup].ReportCompetency rc
ON
rc.Code = rlc.Code and rc.Name = rlc.Name
ALTER TABLE [Central].[Core.Report].[ReportLessonComp] DROP COLUMN CODE
ALTER TABLE [Central].[Core.Report].[ReportLessonComp] DROP COLUMN [Name]
ALTER TABLE [Central].[Core.Report].[ReportLessonComp] DROP COLUMN [Description]
END
GO
When running the if exists \ not exists checks and then select getdate() this works perfeclty fine and gives me the result I expect.
However, when I run the code block above I get error
Msg 207, Level 16, State 1, Line 23
Invalid column name 'Code'.
Msg 207, Level 16, State 1, Line 23
Invalid column name 'Name'.
This script it part of a larger upgrade script and is used in a system calle RoundHouse https://github.com/chucknorris/roundhouse which is the system chosen by the company.
Prior to the above if exists check,
IF (SELECT COUNT(1) FROM sys.columns
WHERE OBJECT_ID = OBJECT_ID('[Central].[Core.Report].[ReportLessonComp]')
AND Name in ('Name','Code')) = 2
which also gave the same issue. I have five tables that I need to update and this is going to stop the team from working if I cant resolve this at my next PR
What can I do in order to stop this from causing the upgrade scripts to fail?
EDIT -- The reason I am linking on varchar fields also is because the previous developer did not create relationships between tables, and was just inserting strings into tables rather than relating by ID causing the potential for unlinked \ inconsistent data.
The table edit prior to this creates the new id column, and this script is getting the value and dropping columns that are no longer needed
SQL Server will parse the whole of the statement prior to execution, so the exists check does not protect you from the update being parsed. If the column has already been dropped, that makes the statement invalid and you get a parse error. The update statement would have to be executed as dynamic SQL, sp_execute basically so that the varchar of the update is not directly parsed.
For SQL Server 2016 and above the drop column can be protected a bit more as well:
ALTER TABLE [Central].[Core.Report].[ReportLessonComp] DROP COLUMN IF EXISTS CODE
SQL Server:
Check column if exists when
If True : (Change/Modify) column_name and dataType
If False : Create
Schema name : Setup
Code:
IF EXISTS (SELECT 1 FROM sys.columns
WHERE Name = N'bitIntialBalance'
AND Object_ID = Object_ID(N'Setup.LeaveVacationsSubType'))
BEGIN
ALTER TABLE [Setup].[LeaveVacationsSubType]
ALTER COLUMN intIntialBalance INT NULL;
EXEC sp_RENAME 'Setup.LeaveVacationsSubType.bitIntialBalance', 'intIntialBalance', 'COLUMN';
--ALTER TABLE [Setup].[LeaveVacationsSubType] MODIFY [intIntialBalance] INT; not working
END
GO
IF NOT EXISTS(SELECT 1 FROM sys.columns
WHERE Name = N'intIntialBalance'
AND Object_ID = Object_ID(N'Setup.LeaveVacationsSubType'))
BEGIN
ALTER TABLE [Setup].[LeaveVacationsSubType]
ADD intIntialBalance INT NULL;
END
GO
If I guess correctly, the problem is that query plan is made for the whole script, and SQL Server also checks that it can actually perform all the operations, even if it is inside an if statement. That's why you'll get an error, even if in the reality that statement would never be executed.
One way to get around this issue is to make all those statements dynamic, something like this:
execute ('ALTER TABLE [Setup].[LeaveVacationsSubType] MODIFY [intIntialBalance] INT')
I code this query, but unfortunately, I got this error:
"Argument data type bit is invalid for argument 1 of substring
function."
My Stored Procedure is:
ALTER TABLE A ALTER COLUMN B nvarchar(20);
UPDATE A SET B = CASE WHEN SUBSTRING(B, 1, 2)>1000
THEN '1' + B ELSE B END
I convert my data but again get an error.
Absolutely my update query work if there is not the first one(Alter Table Alter Column).
Can anyone explaine why this occurred and how should I fix it?
This code works:
create table a (b bit);
alter table a alter column b nvarchar(20);
go
update a
set b = substring(b, 1, 2);
This code does not:
create procedure p as
begin
alter table a alter column b nvarchar(20);
update a
set b = substring(b, 1, 2);
end;
Why not? The first code actually changes the table, so the update is correct when it is run. Within the stored procedure, the two statements are compiled -- but not run. That means that the update is compiled, but the table has not changed. Hence you get an error.
Although you could solve this using dynamic SQL, I would instead ask why you are modifying column types in a stored procedure. That seems quite irregular. Normally, stored procedures do not do such modifications.
ALTER table Table_1
ALTER COLUMN Id NVARCHAR(20)
//Then continue...
Does anyone see what's wrong with this code for SQL Server?
IF NOT EXISTS(SELECT *
FROM sys.columns
WHERE Name = 'OPT_LOCK'
AND object_ID = Object_id('REP_DSGN_SEC_GRP_LNK'))
BEGIN
ALTER TABLE REP_DSGN_SEC_GRP_LNK
ADD OPT_LOCK NUMERIC(10, 0)
UPDATE REP_DSGN_SEC_GRP_LNK
SET OPT_LOCK = 0
ALTER TABLE REP_DSGN_SEC_GRP_LNK
ALTER COLUMN OPT_LOCK NUMERIC(10, 0) NOT NULL
END;
When I run this, I get:
Msg 207, Level 16, State 1, Line 3
Invalid column name 'OPT_LOCK'.
on the update command.
Thanks.
In this case you can avoid the problem by adding the column as NOT NULL and setting the values for existing rows in one statement as per my answer here.
More generally the problem is a parse/compile issue. SQL Server tries to compile all statements in the batch before executing any of the statements.
When a statement references a table that doesn't exist at all the statement is subject to deferred compilation. When the table already exists it throws an error if you reference a non existing column. The best way round this is to do the DDL in a different batch from the DML.
If a statement both references a non existing column in an existing table and a non existent table the error may or may not be thrown before compilation is deferred.
You can either submit it in separate batches (e.g. by using the batch separator GO in the client tools) or perform it in a child scope that is compiled separately by using EXEC or EXEC sp_executesql.
The first approach would require you to refactor your code as an IF ... cannot span batches.
IF NOT EXISTS(SELECT *
FROM sys.columns
WHERE Name = 'OPT_LOCK'
AND object_ID = Object_id('REP_DSGN_SEC_GRP_LNK'))
BEGIN
ALTER TABLE REP_DSGN_SEC_GRP_LNK
ADD OPT_LOCK NUMERIC(10, 0)
EXEC('UPDATE REP_DSGN_SEC_GRP_LNK SET OPT_LOCK = 0');
ALTER TABLE REP_DSGN_SEC_GRP_LNK
ALTER COLUMN OPT_LOCK NUMERIC(10, 0) NOT NULL
END;
The root cause of the error is the newly added column name is not reflected in the sys.syscolumns and sys.columns table until you restart SQL Server Management Studio.
For your information,you can replace the IF NOT EXISTS with the COL_LENGTH function. It takes two parameters,
Table Name and
Column you are searching for
If the Column is found then it returns the range of the datatype of the column Ex: Int (4 bytes), when not found then it returns a NULL.
So, you could use this as follows and also combine 3 Statements into one.
IF (SELECT COL_LENGTH('REP_DSGN_SEC_GRP_LNK','OPT_LOCK')) IS NULL
BEGIN
ALTER TABLE REP_DSGN_SEC_GRP_LNK
ADD OPT_LOCK NUMERIC(10, 0) NOT NULL DEFAULT 0
END;
Makes it simpler.
I have a SQL script that populates a temp column and then drops the column at the end of the script. The first time it runs, it works fine because the column exists, then it gets dropped. The script breaks the 2nd time because the column no longer exists, even though the IF statement ensures that it won't run again. How do I get around SQL checking for this field?
IF EXISTS (SELECT name FROM syscolumns
WHERE name = 'COLUMN_THAT_NO_LONGER_EXISTS')
BEGIN
INSERT INTO TABLE1
(
COLUMN_THAT_NO_LONGER_EXISTS,
COLUMN_B,
COLUMN_C
)
SELECT 1,2,3 FROM TABLE2
ALTER TABLE TABLE1 DROP COLUMN COLUMN_THAT_NO_LONGER_EXISTS
END
I had a similar problem once and got round it by building all the queries as strings and executing them using the Exec() call. That way the queries (selects, inserts or whatever) don't get parsed till they are executed.
It wasn't pretty or elegant though.
e.g
exec('INSERT INTO TABLE1(COLUMN_THAT_NO_LONGER_EXISTS,COLUMN_B,COLUMN_C) SELECT 1,2,3 FROM TABLE2')
Are you checking the column isnt on another table ? If not you probably to check the table too see if statement below.
If you are already doing that is it running a in a single transaction and not picking up the that dropped column has gone ?
IF Not EXISTS (SELECT name FROM sys.columns
WHERE name = 'COLUMN_THAT_NO_LONGER_EXISTS' and Object_Name(object_id) = 'Table1')
Created a quick script program for this; can you confirm this matches what you are trying to do because in SQL 2007 at least this isnt returning an error. If i create the table and run through with teh alter table to add colc it works; if i then run the if / insert that works even after dropping the table.
create table tblTests
(
TestID int identity (1,1),
TestColA int null,
TestColB int null
)
go -- Ran this on its own
insert into tblTests (TestColA, TestColB)
Select 1,2
go 10
-- Insert some initial data
alter table tblTests
add TestColC Int
go -- alter the table to add new column
-- Run this with column and then after it has removed it
IF EXISTS (SELECT name FROM sys.columns a
WHERE name = 'TestColC' AND
OBJECT_NAME(object_id) = 'tblTests')
Begin
insert into tblTests (TestColA, TestColB, testcolc)
select 1,2,3
alter table tblTests
drop column TestColC
End