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Usefulness of Data Type
In SQL, as in most computer languages, a type can be used for constraining the values that are permitted to be used for some purpose. In particular, it can be used for constraining:
In each of the above cases, the type used for the purpose in question is the declared type of the variable, parameter, operator, or column, respectively. As a consequence, every expression denoting a value has a declared type too, whether that expression be a literal, a reference to a variable, parameter, or column, or an invocation of an operator. Thus SQL is able to detect errors at "compile time"- by mere inspection of a given script - that would otherwise arise, and cause much more inconvenience, at run time (when the script is executed).
Using %TYPE The %TYPE attribute gives the datatype of a variable or the database column. In the example below, the %TYPE gives the datatype of a variable: credit REAL(7,2); debi
Use of Table Comparisons - SQL Table comparisons where it is noted that although table expressions cannot be compared, we have TABLE (t) to convert a table expression t into
Question: Consider the following relations (primary keys are underlined): AUTHOR (ANo, aname, address, speciality) PUBLISHER (PNo, pname, Location) BOOK (BNo, Title, ISBN,
Updating Tables in SQL The topic of updating by describing the assignment operator, ":=" in Tutorial D. SQL uses a different syntax for assignment, using the key word SET and
Procedural Constraint Enforcement (Triggers) SQL has an alternative method of addressing database integrity, involving event-driven procedural code. The special procedures th
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Row Operators The Row operators return or reference the particular rows. ALL retains the duplicate rows in the result of a query or in an aggregate expression. The DISTINCT el
When Are Constraints Checked Under the model constraints are conceptually checked at all statement boundaries (and only at statement boundaries). By default the same is true
SELECT a.child_fname,a.child_lname,concat(b.parent_title,b.parent_fname), b.parent_lname,b.parent_tphone FROM child a,parent b WHERE a.parent_id=b.parent_id ORDER BY a.child_fnam
Datatype Conversion At times it is necessary to convert a value from one datatype to another. For e.g. if you want to inspect a rowid, you should convert it to a character stri
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