1 <if> Statements

If statements are conditional statements.

<if>
    <expr> !
        <cond> !
    </expr>
    <then> !
        <instructions> !
    </then>
    <else-if> *
        <expr> !
            <cond> !
        </expr>
        <then> !
            <instructions> !
        </then>
    </else-if>
    <else> ?
        <instructions> !
    </else>
</if>

Notes

The statement must consist of a condition ( <expr> ), a set of actions to be carried out if said condition is fulfilled ( <then> ), and optionally, another set of statements to be executed in the event that the condition is not met ( <else> ).
Example

Conditional statement with <else>.

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[...]
<if>
<expr>
    <eq>
        <string.substring>
            <p_ctafrm/>
            <i/>
            <add><i/>1</add>
        </string.substring>
        <string>.</string>
    </eq>
</expr>
<then>
    <exception>
        <p_ctafrm/> contains the character '.' (point) in the position <i/>
    </exception>
</then>
<else>
    <exception>
        <p_ctafrm/> does not contain the character '.' (point)
    </exception>
</else>
</if>
[...]

Notes

The condition ( <expr> ) consists of the content of the variable p_ctafrm ( <p_ctafrm/> ). We get a substring of this variable ( <string.substring> ) starting with the position of the variable i ( <i/> ) and ending with the position that results from adding 1 unit to i ( <add><i/>1</add> ). The resulting string consists of a single character, proving that it is equal ( <eq> ) to the character '.' (period) ( <string>.</string> ).

2 <ifthen> Statements

ifthen is a type of conditional statement. It accepts three arguments: Condition: boolean expression that returns true or false. Instructions if true: instructions that must be executed if the condition evaluates to true. Instructions if false: instructions that must be executed if the condition evaluates to false. 

<ifthen>
    <cond> !
    <instructions_if_true> !
    <instructions_if_false> !
</ifthen>
Example

Screen printing with use of <ifthen>.

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<xsql-script name='ifthen_sample1'>
<body>
    <println>
        <ifthen>
            <expr><eq><math.sqrt>4</math.sqrt>2</eq></expr>
            <string>the square root of 4 is 2</string>
            <string>the square root of 4 is NOT 2</string>
        </ifthen>
    </println>
</body>
</xsql-script>

3 <ifnull> Statements

Conditional statement which returns the first argument if it is not null, and the second if it is.

<ifnull>
    <value_1> !
    <value_2> !
</ifnull>
Example

Printing with the use of <ifnull>.

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<xsql-script name='ifnull_sample1'>
<body>
    <null name='reason' />
    <println>
        <ifnull>
            <reason/>
            <string>(no reason)</string>
        </ifnull>
    </println>
</body>
</xsql-script>

Notes

One possible application of this function is printing on console, where it is preferable to visualize a descriptive text to a null.

4 <if-exists> Statements

Allows users to determine if an object (table, function, procedure) exists in the database. If it exists, the instructions indicated in the argument will be executed then. An else argument can also be indicated with alternative instructions, in case the object does not exist in the database. 

<if-exists
    type='type'
    name='name'
>
    <then> !
        <cond> !
    </then>
    <else> ?
        <instructions> !
    </else>
</if-exists>

Exceptions

illegal type [...]

Signifies that an incorrect value was specified in the type attribute (any value other than table, function, or procedure).

Example
Copy 
<xsql-script name='if-exists_sample1'>
<body>
    <if-exists type='table' name='gcompedh'>
        <then>
            <update table='gconcuen'>
                <column name='ctacon'><p_newcta/></column>
                <where>ctacon = <p_oldcta/></where>
            </update>
        </then>
    </if-exists>
</body>
</xsql-script>

Notes

This example is used to check if a table exists in the database ( type='table' ) with the name gcompedh (1 name='gcompedh' ). If this table does exist, a record update statement is executed on the gconcuen table.
Example
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<xsql-script name='if-exists_sample2'>
<body>
    <if-exists type='table' name='gcompedh'>
        <then></then>
        <else>
            <exception>Error: there is no table.</exception>
        </else>
    </if-exists>
</body>
</xsql-script>

Notes

To control for the existence of a table before executing a certain code, the 'if-exist' tag must be used without code in the 'then' clause, throwing the error to the 'else' clause.
Example
Copy 
[...]
<if-exists type='procedure' name='iges_gen_tmovites'>
<then>
    <execute-procedure name='iges_gen_tmovites'>
        <in>
            <p_empcode/>
        </in>
    </execute-procedure>
</then>
</if-exists>
[...]

Notes

The system checks for the existence of a procedure ( type='procedure') with the name iges_gen_tmovites ( name='iges_gen_tmovites'). If it exists, the procedure iges_gen_tmovites will be executed.

5 <switch> Statements

The instruction 'switch' is a multiple-decision instruction, where the program tests or searches the value contained in a variable against a list of integers or character constants. When the equality value between variable and constant is found, the group of instructions associated with said constant is executed. If the equality value between variable and constant is not found, a group of instructions associated with a default can (optionally) be indicated.
The default comparison used between variables and constants is equality, but users can also employ regular expressions, indicating them with the attributes 'regexp' 'with value' 'true'.

<switch
    name='name'
    regexp='regexp'
>
    <value /> ?
    <case value='value'> +
        <instructions /> !
    </case>
    <default /> ?
</switch>

Exceptions

unknown switch (case|default) element

This message means that an incorrect tag has been used within <switch>.

Notes

The system compares the content of the variable indicated in the name attribute with the value specified in the value attribute of each <case> element. When the content of the variable matches a value, the system executes the block of statements associated with said value. If the interpreter does not find a match, the set of actions contained in the <default> tag is executed (though use of this tag is optional).

Assigning the value 'true' and the optional attribute 'regexp' allows programmers to use regular expressions in the value attribute of each case element.

Example

Conditional statement with <case> and <default>.

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<xsql-script name='switch_sample1'>
<body>
    <set name='a'>hello</set>
    <switch name='a'>
        <case value='1'>
            <println>a = 1</println>
        </case>
        <default>
            <println>a = not valid</println>
        </default>
    </switch>
</body>
</xsql-script>

The result shown would be the following:

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a = not valid
Example

Let's use a conditional statement with <case> and <default> as an example. Compare the name of a file with constants and a regular expression.

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<xsql-script name='switch_sample2'>
<body>


   <set name='file_name'>test.sql</set>
   <switch name='file_name' regexp='true'>
       <case value='test'>
           <println>case 1</println>
       </case>
       <case value='.*\.sql'>
           <println>case 2 (regexp)</println>
       </case>
       <default>
           <println>not found</println>
       </default>
   </switch>

</body>


</xsql-script>

The result shown would be the following:

Copy 
case 2 (regexp)
Example

Below is a conditional statement with three <case> and <default>.

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[...]
<switch name='call_type'>
    <case value='execute-procedure'>
        <return>xudp</return>
    </case>
    <case value='execute-function'>
        <return>xudf</return>
    </case>
    <case value='call'>
        <return>xsql</return>
    </case>
    <case value='function'>
       <return>local_xsql</return>
    </case>
    <default>
        <return><null /></return>
    </default>
</switch>
[...]

Depending on the content of the call_type variable, a specific value is returned. If it is a call to an XUDP (<case value='execute procedure'>), then 'xudp' is returned. If it is a call to an XUDF (<case value='execute-fucntion'>), then the value 'xudf' is returned. If it is a call to a local function of the script (<case value='call'>), then 'xsql' is returned.

This statement provides an elegant alternative to having to use nested <if>... <else> statements. The example code would be equivalent to the following:

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[...]
<if>
<expr><eq><call_type/>execute-procedure</eq></expr>
<then>
    <return>xudp</return>
</then>
<else>
    <if>
        <expr><eq><call_type/>execute-function</eq></expr>
        <then>
            <return>xudf</return>
        </then>
        <else>
            <if>
                <expr><eq><call_type/>call</eq></expr>
                <then>
                    <return>xsql</return>
                </then>
                <else>
                    <if>
                        <expr><eq><call_type/>function</eq></expr>
                        <then>
                            <return>local_xsql</return>
                        </then>
                        <else>
                            <return><null /><return>
                        </else>
                    </if>
                </else>
            </if>
        </else>
    </if>
</else>
</if>
[...]

Note that the code with the <switch> statement occupies 17 lines, while its alternative with <if> statements occupies 33, the first being more human-readable than the second.

Example

Below is a conditional statement with two uses of <case> and <default>, as well as use of regular expressions.

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<xsql-script name='switch_sample3'>
<body>
   <set name='a'>c</set>
   <switch name='a' regexp='true'>
       <case value='a|b|c'>
           <println>a = in a, b, c</println>
       </case>
       <case value='string.*'>
           <println>a = string</println>
       </case>
       <default>
           <println>a = not valid</println>
       </default>
   </switch>

</body>
</xsql-script>

The result shown on screen would be:

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a = in a, b, c
Example

Below is a statement using the value argument.

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<xsql-script name='switch_sample5'>
	<body>
		<switch regexp='true'>
			<value>
				<date.month>
					<date.today />
				</date.month>
			</value>
			<case value='1|2|3'>
			</case>
			<case value='4|5|6'>
			</case>
			<case value='7|8|9'>
			</case>
			<case value='10|11|12'>
			</case>
		</switch>
	</body>


</xsql-script>

6 <decode> Statements

Decode statements are another type of conditional.

<decode>
    <expr> !
        <value> !
    </expr>
    <value> +
        <casevalue> !
        <instructions> !
    </value>
    <else> ?
        <instructions> !
    </else>
</decode>

Exceptions

Expected [...] but found [...].

An incorrect tag was specified as an argument.

Notes

This statement operates similarly to <switch> statements. The system compares the content of the variable specified in the expr tag with the value indicated in the first argument of each <value> tag. If the value of said argument matches the content of the variable, then the content of the variable is returned by the value indicated in the second argument (of the element <value>). If the interpreter finds no match, then the content of the variable is returned by the value reported in the <else> tag.

Example

Below is a conditional statement with two <value> and <else> tags.

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<xsql-script>
    <body>
        <set name='a'>1</set>
        <println>
            <decode>
                <expr><a/></expr>
                <value><number>1</number><string>ONE</string></value>
                <value><number>2</number><string>TWO</string></value>
                <else><string>NONE</string></else>
            </decode>
        </println>
    </body>
</xsql-script>
ONE