More questions about porting from MySQL to MS SQL

[Ted]

1) In several tables, in my MySQL version, I created columns using
something like the following:

`ab_timestamp` timestamp NOT NULL default CURRENT_TIMESTA MP on update
CURRENT_TIMESTA MP,

This allowed me to ensure that when a record is either added or edited,
the value in the field is set to the current date and time. I.E.,
ab_timestamp is given the current date and time when a record is
created, and then it is updated to the date and time at which the
record is updated. I learned the hard way that MS SQL does not like
"on update CURRENT_TIMESTA MP". So, it looks like MS SQL will allow me
to initialize ab_timestamp to the current date and time, but not
automatically update it to the date and time at which the record is
updated. I have plenty of code to port that depends on the behaviour
supported by MySQL. DO I have to modify all that code, or is there a
way to get MS SQL to provide it? (Yes, I know 'timestamp' is
deprecated in MS SQL and that I should use datetime instead, and in
fact have already done so.)

2) I began with a single SQL script that creates all the tables, views,
functions and triggers the database needs. On trying to get MS SQL to
accept it, I encountered a number of error messages saying that CREATE
FUNCTION and CREATE VIEW need to be the first statement in a script.
Why? I know I can work around this odd constraint by putting each
function and view (and IIRC trigger) into its own script, but that
seems like a make work effort imposed for some unknown reason by MS
SQL, unless there is another way to get around it.

3) I see, in the documentation for CREATE FUNCTION, functions are not
allowed to use a timestamp for either a parameter or a return value.
This is in reference to a pair of scalar functions I am using which
need to manipulate date and time values. For the purpose of
clarification, is this documentation refering to all date/time data
types, or only the deprecated timestamp type? As examples, consider
one function that needs to return the most recent date in a date column
in a specific table, or another function that computes a date from a
date and an offset (e.g. if called with the value returned by the first
function as the first argument and '-7' as the second, returns the date
of the day that is a week earlier than that date). These two functions
are frequently used in the SQL code I'm trying to port and I really
don't want to complicate so many of those statements if I don't have
to.

Thanks

Ted

[David Portas]

Re: More questions about porting from MySQL to MS SQL

Ted wrote:

1) In several tables, in my MySQL version, I created columns using
something like the following:
>
`ab_timestamp` timestamp NOT NULL default CURRENT_TIMESTA MP on update
CURRENT_TIMESTA MP,
>
This allowed me to ensure that when a record is either added or edited,
the value in the field is set to the current date and time. I.E.,
ab_timestamp is given the current date and time when a record is
created, and then it is updated to the date and time at which the
record is updated. I learned the hard way that MS SQL does not like
"on update CURRENT_TIMESTA MP". So, it looks like MS SQL will allow me
to initialize ab_timestamp to the current date and time, but not
automatically update it to the date and time at which the record is
updated. I have plenty of code to port that depends on the behaviour
supported by MySQL. DO I have to modify all that code, or is there a
way to get MS SQL to provide it? (Yes, I know 'timestamp' is
deprecated in MS SQL and that I should use datetime instead, and in
fact have already done so.)
>
2) I began with a single SQL script that creates all the tables, views,
functions and triggers the database needs. On trying to get MS SQL to
accept it, I encountered a number of error messages saying that CREATE
FUNCTION and CREATE VIEW need to be the first statement in a script.
Why? I know I can work around this odd constraint by putting each
function and view (and IIRC trigger) into its own script, but that
seems like a make work effort imposed for some unknown reason by MS
SQL, unless there is another way to get around it.
>
3) I see, in the documentation for CREATE FUNCTION, functions are not
allowed to use a timestamp for either a parameter or a return value.
This is in reference to a pair of scalar functions I am using which
need to manipulate date and time values. For the purpose of
clarification, is this documentation refering to all date/time data
types, or only the deprecated timestamp type? As examples, consider
one function that needs to return the most recent date in a date column
in a specific table, or another function that computes a date from a
date and an offset (e.g. if called with the value returned by the first
function as the first argument and '-7' as the second, returns the date
of the day that is a week earlier than that date). These two functions
are frequently used in the SQL code I'm trying to port and I really
don't want to complicate so many of those statements if I don't have
to.
>
Thanks
>
Ted

1) You can use an UPDATE trigger to simulate the same functionality.
Usually though it is better to use stored procedures to perform all
your data access. That way you can easily include the timestamp as part
of your update procs.

2) You don't need separate scripts for each View / Function. You do
need separate batches. A batch is separated using the GO keyword in
Query Analyzer.

3) Don't confuse TIMESTAMP with DATETIME. They are not at all the same!
You are referring to DATETIME values, which ARE permitted as parameters
and return values in functions. BTW, you don't need to write a function
to do date arithmetic - it already exists as a built-in function:
DATEADD().

--
David Portas, SQL Server MVP

Whenever possible please post enough code to reproduce your problem.
Including CREATE TABLE and INSERT statements usually helps.
State what version of SQL Server you are using and specify the content
of any error messages.

SQL Server Books Online:

http://msdn2.microsoft.com/library/ms130214(en-US,SQL.90).aspx

--

[Erland Sommarskog]

Re: More questions about porting from MySQL to MS SQL

Ted (r.ted.byers@ro gers.com) writes:

1) In several tables, in my MySQL version, I created columns using
something like the following:
>
`ab_timestamp` timestamp NOT NULL default CURRENT_TIMESTA MP on update
CURRENT_TIMESTA MP,
>
This allowed me to ensure that when a record is either added or edited,
the value in the field is set to the current date and time. I.E.,
ab_timestamp is given the current date and time when a record is
created, and then it is updated to the date and time at which the
record is updated. I learned the hard way that MS SQL does not like
"on update CURRENT_TIMESTA MP". So, it looks like MS SQL will allow me
to initialize ab_timestamp to the current date and time, but not
automatically update it to the date and time at which the record is
updated. I have plenty of code to port that depends on the behaviour
supported by MySQL. DO I have to modify all that code, or is there a
way to get MS SQL to provide it?

You will have to modify all that code. To have to be portable is indeed
painful, and a good start is to pay attention to what is in ANSI standards,
what is commonly supported. And not to the least to what are extensions
added by a certain vendor. My knowledge of ANSI and other engines are
poor (since I live in a sheltered world where I only need to support
SQL Server), but I would suspect that the ON UPDATE clause for the
default constraint is properitary to MySQL.

The way to do this in SQL Server is to use a trigger. Not that triggers
usually are very portable...

You can also modify the UPDATE statements so that they read:

UPDATE tbl
SET ...,
ab_timestamp = DEFAULT,
WHERE ...

I believe this syntax is portable.

(Yes, I know 'timestamp' is deprecated in MS SQL and that I should use
datetime instead, and in fact have already done so.)

timestamp is not deprecated in SQL Server, but it's a completely different
data type, which is used to implement optimistic locking. A timestamp
is an 8-bit value is updated each time the row is updated and it's
unique within the database. Further more timestamp value are monotonically
increasing. But there is no correlation with time. Timestamp is
proprietary to SQL Server, so you should probably stay away from it
entirely.

2) I began with a single SQL script that creates all the tables, views,
functions and triggers the database needs. On trying to get MS SQL to
accept it, I encountered a number of error messages saying that CREATE
FUNCTION and CREATE VIEW need to be the first statement in a script.
Why? I know I can work around this odd constraint by putting each
function and view (and IIRC trigger) into its own script, but that
seems like a make work effort imposed for some unknown reason by MS
SQL, unless there is another way to get around it.

Not a separate script, but a separate batch. Batches are separated with
"go" in all query tools. The graphic tools permit you to specify a
different batch separator.

Why? Because else it would be difficult to tell where a procedure ends.
Say that you have:

CREATE PROCEDURE .... AS
....
CREATE TABLE ....

Is that CREATE TABLE part of the procedure or not? (Yes, if you have
BEGIN END it's clear. But of legacy BEGIN END is not required in
stored procedures.)

3) I see, in the documentation for CREATE FUNCTION, functions are not
allowed to use a timestamp for either a parameter or a return value.

As noted above, there is little reason for your to use the timestamp
data type.


--
Erland Sommarskog, SQL Server MVP, esquel@sommarsk og.se

Books Online for SQL Server 2005 at

http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx

Books Online for SQL Server 2000 at

http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx