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Writing Executable Statements

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Objectives After completing this lesson, you should be able to do the following: Identify lexical units in a PL/SQL block Use built-in SQL functions in PL/SQL Describe when implicit conversions take place and when explicit conversions have to be dealt with Write nested blocks and qualify variables with labels Write readable code with appropriate indentation Use sequences in PL/SQL expressions

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Lexical Units in a PL/SQL Block Lexical units: Are building blocks of any PL/SQL block Are sequences of characters including letters, numerals, tabs, spaces, returns, and symbols Can be classified as: Identifiers: v_fname, c_percent Delimiters: ; , +, - Literals: John, 428, True Comments: --, /* */

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PL/SQL Block Syntax and Guidelines Literals Character and date literals must be enclosed in single quotation marks. Numbers can be simple values or in scientific notation. Statements can span several lines.

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Commenting Code Prefix single-line comments with two hyphens (--). Place multiple-line comments between the symbols /* and */. Example:

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SQL Functions in PL/SQL Available in procedural statements: Single-row functions Not available in procedural statements: DECODE Group functions

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SQL Functions in PL/SQL: Examples Get the length of a string: Get the number of months an employee has worked:

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Using Sequences in PL/SQL Expressions Starting in 11g: Before 11g:

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Data Type Conversion Converts data to comparable data types Is of two types: Implicit conversion Explicit conversion Functions: TO_CHAR TO_DATE TO_NUMBER TO_TIMESTAMP

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Data Type Conversion

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Nested Blocks PL/SQL blocks can be nested. An executable section (BEGIN … END) can contain nested blocks. An exception section can contain nested blocks.

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Nested Blocks: Example

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Variable Scope and Visibility

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Qualify an Identifier

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Determining Variable Scope: Example

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Operators in PL/SQL Logical Arithmetic Concatenation Parentheses to control order of operations Exponential operator (**)

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Operators in PL/SQL: Examples Increment the counter for a loop. Set the value of a Boolean flag. Validate whether an employee number contains a value.

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Programming Guidelines Make code maintenance easier by: Documenting code with comments Developing a case convention for the code Developing naming conventions for identifiers and other objects Enhancing readability by indenting

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Indenting Code For clarity, indent each level of code.

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Quiz You can use most SQL single-row functions such as number, character, conversion, and date single-row functions in PL/SQL expressions. True False

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Summary In this lesson, you should have learned how to: Identify lexical units in a PL/SQL block Use built-in SQL functions in PL/SQL Write nested blocks to break logically related functionalities Decide when to perform explicit conversions Qualify variables in nested blocks Use sequences in PL/SQL expressions