Jim Lawrence
accessd at shaw.ca
Sun Jul 29 12:32:12 CDT 2007
Well said Charlotte. To give ground is dishonorable and it death before dishonor. :-) Jim -----Original Message----- From: accessd-bounces at databaseadvisors.com [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Charlotte Foust Sent: Thursday, July 26, 2007 9:28 AM To: Access Developers discussion and problem solving Subject: Re: [AccessD] Primary Key Best Practices Ah, yes, the classic AccessD method for conquering opposition: willfully misinterpret the responses, deny them any validity, and declare yourself the winner! Widely used by Colby and by Drew on occasion. It amounts to "never mind if we're saying much the same thing, you're WRONG!!" LOL Charlotte Foust -----Original Message----- From: accessd-bounces at databaseadvisors.com [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of jwcolby Sent: Thursday, July 26, 2007 5:58 AM To: 'Access Developers discussion and problem solving' Subject: Re: [AccessD] Primary Key Best Practices >From Charlotte: >>You'd still need an identity field to edit it in SQL Server. <<No, in fact you do not!>> > Yes, you do. The true purpose of a primary key is to uniquely > identify a row. No JIM, you DO NOT. Go to SQL Server (I did!) Create a new table - just two rows is fine (I did) Create two fields (I did) DO NOT create any index whatsoever (I did not) Do NOT create a PK (I did not) Open the table (I did) Enter data (I did) Move off the record so that it stores (I did) Do a couple of more (I did) Edit records (I did) DELETE records (I did) LISTEN VERY CAREFULLY JIM. YOU DO !!!!NOT!!!! HAVE TO HAVE A PK TO DO ANY OF THE THINGS YOU MENTIONED. I have actually done this, apparently you have not. You can have duplicate data, you can have unique data (with a caveat in SQL Server - see below), it simply does NOT MATTER. You can add, edit and delete records in a table in SQL Server without having any keys, candidate or otherwise, and without having any indexes. You need to get off it for a minute and admit that while the model is nice in fact NO RDBMS actually IMPLEMENTS the model. I don't know about you but I actually live in reality and it is important to understand what REALLY HAPPENS out here in the real world. By "your" definition - a candidate key or a PK (which has to be a candidate key) is any field or combination of fields where the data stored in the fields is unique within the table and can therefore be used to uniquely identify the row. YOU can create a table (though you may refuse to do so in order to avoiding admitting this, but I HAVE DONE SO) where there is NO candidate key or PK, and in fact the data in those two fields are exactly the same in some records. You CAN still edit data directly from inside of SQL Server. You can still add records (programmatically with a query), you can still delete records (programmatically with a query), you can still edit records (programmatically, with a query). JIM, I HAVE DONE THIS! You do NOT have to have a PK in order to do ADD EDIT OR DELETE rows in a REAL LIFE record in a REAL LIFE DATABASE, and MODEL BE DAMNED! If the model LIES, then it is time to pay more careful attention to reality. Models MODEL reality, not vice versa. NOW... Make two rows in the table identical. SQL Server complains (Access does not btw). You CAN move off of the record, storing the data. However you cannot delete OR EDIT either record (in SQL Server you are screwed apparently, you CAN in Access). You CAN still add new records though (even in SQL Server), and you CAN edit those OTHER records as long as those other records are unique, even in SQL Server. What does this prove? SQL Server has a bug, whereas Access does not. Any way you look at it, SQL Server has a bug, either in allowing the identical data to store, or not allowing the data to be edited later. Notice that: 1) The data STORED whether or not it was unique. 2) EVEN with non unique records in place, more data could be added, edited and deleted (even in SQL Server). 3) Access could delete or modify the data, even the records where the data is not unique, SQL could not. Now, scream all you want Jim, but facts is facts and REAL DBMSs do NOT require a candidate key or a PK in order to add, delete or edit the data in a table. BY YOUR OWN DEFINITION, a PK or candidate key is one where ALL THE DATA in a field or set of fields is unique. BOTH Access and SQL Server can add records, wither the data is unique or not. BOTH databases can add new records whether or not there is data in the table that prevents defining a candidate key or a PK. ACCESS can edit data even in records where the data is exactly the same as another record. JIM, I HAVE DONE THIS! You do NOT have to have a PK in order to ADD EDIT OR DELETE rows in a REAL LIFE record in a REAL LIFE TABLE in a REAL LIFE DATABASE, and MODEL BE DAMNED! If the model LIES, then it is time to pay more careful attention to reality. Models MODEL reality, not vice versa. YOU CLAIM that without a PK you cannot edit data in a relational database. YOU CLAIM that a PK is by necessity a field or set of fields where the data is unique throughout the table. I HAVE PROVEN that your claims are not true! Go ahead Jim, sputter away about how reality doesn't correctly implement the model, that is true, and that is irrelevant. Reality is, and NO RDBMS correctly implements the model in all aspects, and you know that. And (to the immense relief of everyone I am sure) I am SOOOOO done with you and your model and this discussion. John W. Colby Colby Consulting www.ColbyConsulting.com -----Original Message----- From: accessd-bounces at databaseadvisors.com [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Jim Dettman Sent: Thursday, July 26, 2007 7:28 AM To: 'Access Developers discussion and problem solving' Subject: Re: [AccessD] Primary Key Best Practices <<No, in fact you do not!>> Yes, you do. The true purpose of a primary key is to uniquely identify a row. You may not have indicated in the RDBMS system a single index or that any field or fields is a "PK" for the relation, but you are still using one anytime you add or edit the data. The question is: If your going to edit a row, how do you as a user identify which row it is that you need to change? You use the data in the fields combined in a certain way to know that you are editing the correct row. It may mean that you might have to use every field (what is sometimes called a super-key), but you do use a key even if you have not defined one in the RDBMS. If you cannot identify a row uniquely, then storing the data is basically meaningless. This goes to the heart of the point that I was making that a "primary key" is much more then a pointer. It relates to the meaning of the data, not how it's stored. Jim. -----Original Message----- From: accessd-bounces at databaseadvisors.com [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of jwcolby Sent: Wednesday, July 25, 2007 7:56 PM To: 'Access Developers discussion and problem solving' Subject: Re: [AccessD] Primary Key Best Practices Charlotte, >You'd still need an identity field to edit it in SQL Server. No, in fact you do not! I have all these huge 1 table databases that I am currently using. They are lists of people / addresses / information about the people. They stand alone, at least initially. I always create an ANPK but... I just created a table in SQL server consisting of two fields char(10), text1 and text2. I saved the table, then I opened the table and edited the data, directly in SQL Server. No PK, I could edit the data. I entered new data records, I went back and edited existing data. I deleted rows. I can do any of the things that you are saying cannot be done, with out a PK, or even an index. Just plain old simple char() fields. Not an index in sight, never mind a unique index. No PK. I can add records, I can edit existing records, I can delete records, directly in the table in SQL Server. In fact my client used these huge data tables (lists of addresses) to create name / address lists that they sold to their clients long before I ever hit the scene. Just one table. They did not understand nor care about PKs. There were no child tables so no pointer was needed to get back to the parent. No unique index can be created, because there are in fact duplicates. They create hashes in order to discover and get rid of the duplicates in the output but there is no field, nor combination of fields that uniquely identify a specific record. The client uses (makes a LOT OF MONEY) off of these tables. Is this a database? I can't answer that. It is a standalone (extremely large) table in a big iron database management system. It generates millions of dollars a year for the owners. They do not in fact ever edit it, but they could if they wanted to, at least inside of SQL Server. John W. Colby Colby Consulting www.ColbyConsulting.com -----Original Message----- From: accessd-bounces at databaseadvisors.com [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Charlotte Foust Sent: Wednesday, July 25, 2007 5:50 PM To: Access Developers discussion and problem solving Subject: Re: [AccessD] Primary Key Best Practices You're picking nits, John. You'd still need an identity field to edit it in SQL Server. If the unique key exists, you have a functional PK, whether you call it that or not. Charlotte Foust -----Original Message----- From: accessd-bounces at databaseadvisors.com [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of jwcolby Sent: Wednesday, July 25, 2007 2:47 PM To: 'Access Developers discussion and problem solving' Subject: Re: [AccessD] Primary Key Best Practices Any database made up of a single table would not require a PK. John W. 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