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| pickettwayne |
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pickettwayne
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| supZ |
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supZ
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 Posted: 12:15 - 13 Apr 2010  Post subject: |
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what a bollocks question 
where's this from?
good language or not its the only one we've got as far as i know 
mssql, mysql, oracle, sybase, etc.. all use variations of SQL/a structured query language.
not heard of any other way of retrieving data.
used various databases/various styles of SQL and i've never found a problem i couldnt solve with it. well, there are limitations on certain types of sql (like there are things mysql cant do that mssql/t-sql can and the like) but as a language id say its a good one.
easy to read, work with... if you know it of course
not sure why its saying that null is a problem in a db either.. you can choose to allow nulls or not, pick default values to avoid nulls and use functions to replace nulls such as 'ISNULL(fieldname,0)' <-- replaces any nulls in fieldname with a 0.
so yeh.. no problems as far as i can see.
weird question... 
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| FreshAL |
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FreshAL
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Joined: 04 Jul 2005
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| Posted: 12:33 - 13 Apr 2010 Post subject: |
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1) That's a tough question. What's it for, A level or degree?
Short answer is that implementations of SQL do violate the relational model
2) You are a lazy fucker. 30 seconds on Google gets this
https://en.wikipedia.org/wiki/Relational_model which has a great section listing all of the problems with SQL and the relational model.
| Quote: | SQL and the relational model
SQL, initially pushed as the standard language for relational databases, deviates from the relational model in several places. The current ISO SQL standard doesn't mention the relational model or use relational terms or concepts. However, it is possible to create a database conforming to the relational model using SQL if one does not use certain SQL features.
The following deviations from the relational model have been noted in SQL. Note that few database servers implement the entire SQL standard and in particular do not allow some of these deviations. Whereas NULL is ubiquitous, for example, allowing duplicate column names within a table or anonymous columns is uncommon.
Duplicate rows
The same row can appear more than once in an SQL table. The same tuple cannot appear more than once in a relation.
Anonymous columns
A column in an SQL table can be unnamed and thus unable to be referenced in expressions. The relational model requires every attribute to be named and referenceable.
Duplicate column names
Two or more columns of the same SQL table can have the same name and therefore cannot be referenced, on account of the obvious ambiguity. The relational model requires every attribute to be referenceable.
Column order significance
The order of columns in an SQL table is defined and significant, one consequence being that SQL's implementations of Cartesian product and union are both noncommutative. The relational model requires there to be no significance to any ordering of the attributes of a relation.
Views without CHECK OPTION
Updates to a view defined without CHECK OPTION can be accepted but the resulting update to the database does not necessarily have the expressed effect on its target. For example, an invocation of INSERT can be accepted but the inserted rows might not all appear in the view, or an invocation of UPDATE can result in rows disappearing from the view. The relational model requires updates to a view to have the same effect as if the view were a base relvar.
Columnless tables unrecognized
SQL requires every table to have at least one column, but there are two relations of degree zero (of cardinality one and zero) and they are needed to represent extensions of predicates that contain no free variables.
NULL
This special mark can appear instead of a value wherever a value can appear in SQL, in particular in place of a column value in some row. The deviation from the relational model arises from the fact that the implementation of this ad hoc concept in SQL involves the use of three-valued logic, under which the comparison of NULL with itself does not yield true but instead yields the third truth value, unknown; similarly the comparison NULL with something other than itself does not yield false but instead yields unknown. It is because of this behaviour in comparisons that NULL is described as a mark rather than a value. The relational model depends on the law of excluded middle under which anything that is not true is false and anything that is not false is true; it also requires every tuple in a relation body to have a value for every attribute of that relation. This particular deviation is disputed by some if only because E.F. Codd himself eventually advocated the use of special marks and a 4-valued logic, but this was based on his observation that there are two distinct reasons why one might want to use a special mark in place of a value, which led opponents of the use of such logics to discover more distinct reasons and at least as many as 19 have been noted, which would require a 21-valued logic.[citation needed] SQL itself uses NULL for several purposes other than to represent "value unknown". For example, the sum of the empty set is NULL, meaning zero, the average of the empty set is NULL, meaning undefined, and NULL appearing in the result of a LEFT JOIN can mean "no value because there is no matching row in the right-hand operand". |
Read this by way of atonement - https://en.wikipedia.org/wiki/Tuple_relational_calculus
and I will give you a right good  slapping if you don't google before asking next time |
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| pickettwayne |
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pickettwayne
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Joined: 19 Feb 2008
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| Posted: 12:46 - 13 Apr 2010 Post subject: |
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Its for a degree. Actually, looking on Google and Wikipedia was the first thing I done. However, I don't take Wikipedia for granted and i just use it as a pointer to other sources. I just wanted to know what other people real life experiences and opinions were. So, its not exactly being a lazy fucker. I should of mentioned that I looked on Google and Wikipedia first but I thought people would of taken that for granted. 
| FreshAL wrote: | 1) That's a tough question. What's it for, A level or degree?
Short answer is that implementations of SQL do violate the relational model
2) You are a lazy fucker. 30 seconds on Google gets this
https://en.wikipedia.org/wiki/Relational_model which has a great section listing all of the problems with SQL and the relational model.
| Quote: | SQL and the relational model
SQL, initially pushed as the standard language for relational databases, deviates from the relational model in several places. The current ISO SQL standard doesn't mention the relational model or use relational terms or concepts. However, it is possible to create a database conforming to the relational model using SQL if one does not use certain SQL features.
The following deviations from the relational model have been noted in SQL. Note that few database servers implement the entire SQL standard and in particular do not allow some of these deviations. Whereas NULL is ubiquitous, for example, allowing duplicate column names within a table or anonymous columns is uncommon.
Duplicate rows
The same row can appear more than once in an SQL table. The same tuple cannot appear more than once in a relation.
Anonymous columns
A column in an SQL table can be unnamed and thus unable to be referenced in expressions. The relational model requires every attribute to be named and referenceable.
Duplicate column names
Two or more columns of the same SQL table can have the same name and therefore cannot be referenced, on account of the obvious ambiguity. The relational model requires every attribute to be referenceable.
Column order significance
The order of columns in an SQL table is defined and significant, one consequence being that SQL's implementations of Cartesian product and union are both noncommutative. The relational model requires there to be no significance to any ordering of the attributes of a relation.
Views without CHECK OPTION
Updates to a view defined without CHECK OPTION can be accepted but the resulting update to the database does not necessarily have the expressed effect on its target. For example, an invocation of INSERT can be accepted but the inserted rows might not all appear in the view, or an invocation of UPDATE can result in rows disappearing from the view. The relational model requires updates to a view to have the same effect as if the view were a base relvar.
Columnless tables unrecognized
SQL requires every table to have at least one column, but there are two relations of degree zero (of cardinality one and zero) and they are needed to represent extensions of predicates that contain no free variables.
NULL
This special mark can appear instead of a value wherever a value can appear in SQL, in particular in place of a column value in some row. The deviation from the relational model arises from the fact that the implementation of this ad hoc concept in SQL involves the use of three-valued logic, under which the comparison of NULL with itself does not yield true but instead yields the third truth value, unknown; similarly the comparison NULL with something other than itself does not yield false but instead yields unknown. It is because of this behaviour in comparisons that NULL is described as a mark rather than a value. The relational model depends on the law of excluded middle under which anything that is not true is false and anything that is not false is true; it also requires every tuple in a relation body to have a value for every attribute of that relation. This particular deviation is disputed by some if only because E.F. Codd himself eventually advocated the use of special marks and a 4-valued logic, but this was based on his observation that there are two distinct reasons why one might want to use a special mark in place of a value, which led opponents of the use of such logics to discover more distinct reasons and at least as many as 19 have been noted, which would require a 21-valued logic.[citation needed] SQL itself uses NULL for several purposes other than to represent "value unknown". For example, the sum of the empty set is NULL, meaning zero, the average of the empty set is NULL, meaning undefined, and NULL appearing in the result of a LEFT JOIN can mean "no value because there is no matching row in the right-hand operand". |
Read this by way of atonement - https://en.wikipedia.org/wiki/Tuple_relational_calculus
and I will give you a right good slapping if you don't google before asking next time |
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| FreshAL |
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FreshAL
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Joined: 04 Jul 2005
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Old Thread Alert!
The last post was made 16 years, 143 days ago. Instead of replying here, would creating a new thread be more useful? |
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