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Data Types in SQL - Character
CHARACTER or, synonymously, CHAR, for character strings. When this type is to be the declared type of something (e.g., a column), the permissible values are further constrained by a maximum length specification given in parentheses and optionally by the key word VARYING, indicating that values shorter than the maximum, including the empty string '' , are also permissible. Examples: CHAR(5) for strings of five characters only, CHARACTER VARYING (100), which can be abbreviated to VARCHAR(100), for strings of up to one hundred characters. The last two are alternative spellings for the same declared type.
The type CHARACTER LARGE OBJECT, or CLOB, allows for inclusion of strings that are longer than the longest supported by the other CHARACTER types. Note that in the terminology of the theory book CHARACTER is a kind of type generator. The key word does not of itself denote a type, but only does so when qualified by a length specification. A similar remark applies to some of the other type names used in SQL.
Case Sensitivity Similar to all the identifiers, the variables, the names of constants, and parameters are not case sensitive. For illustration, PL/SQL considers the following n
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
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
Naming Conventions The similar naming conventions apply to all PL/SQL program items and units including the variables, cursors, constants, cursor variables, procedures, exception
Avoiding Collection Exceptions In many cases, if you reference a nonexistent collection element, then PL/SQL raises a predefined exception. Consider the illustration shown b
Cursor Variables Similar to a cursor, cursor variable points to the current row in the result set of a multi-row query. But, dissimilar a cursor, a cursor variable can be opene
Bulk Fetching The illustration below shows that you can bulk-fetch from a cursor into one or more collections: DECLARE TYPE NameTab IS TABLE OF emp.ename%TYPE; TYPE S
"Not Enforced" Table Constraints A constraint that is not enforced is not really a constraint within the meaning of the act, but SQL does have such a concept and it needs to b
MERGE and TRUNCATE in SQL SQL has two more table update operators, MERGE and TRUNCATE. MERGE, like INSERT, takes a source table s and uses it to update a target table t. Brief
Defining and Declaring Collections To create the collections, you must define a collection type, and then declare the collections of that type. You can define the VARRAY types a
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