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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).
Updating Objects: To change the attributes of objects in an object table, you can use the UPDATE statement, as the illustration below shows: BEGIN UPDATE persons p SET p
The SQL ‘CREATE TABLE' scripts for all the tables you have implemented. Note that your tables must correspond exactly to the ERD you have provided in 1. above, or you will lose ma
Using INNER JOIN INNER JOIN is used to retrieve the data from all tables listed based on a condition of equality listed after keyword ON. If the condition is not meet, rows ar
Relational Algebra - SQL It describes some operators, that together constitute an algebra that is not only relationally complete but also irreducibly so (very nearly- apart f
UPDATE Statement The UPDATE statement transforms the values of the specified columns in one or more rows in the table or view. Syntax:
Conditionals - SQL At first sight SQL does not appear to have a single operator for expressing logical implication. In this respect it would be in common with most programming
Using LOCK TABLE You use the LOCK TABLE statement to lock the whole database tables in the specified lock mode so that you can share or deny the access to them. For illustrati
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Example of Foreign Key Constraint Example: Alternative formulation for 6.3 as a foreign key constraint ALTER TABLE EXAM_MARK ADD CONSTRAINT Must_be_enrolled_to_take_exam
Using NOT NULL Besides assigning an initial value, the declarations can impose the NOT NULL constraint, as the example below shows: acct_id INTEGER(4) NOT NULL := 9999; You ca
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