v5r4 sql enhancements

7/30/2019 V5R4 SQL Enhancements

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V5R4 SQL Enhancements

Programming - SQL

Written by Mike Faust

Tuesday, 09 May 2006 18:00

With V5R4, IBM continues its expansion of Structured Query Language (SQL) support inside of DB2Universal Database (DB2 UDB) for iSeries. These enhancements include additional scalar and

aggregate functions, new data types, support for online analytical processing (OLAP), and support for

embedded SQL in free-format ILE RPG. In this article, we'll explore these changes and see how they'llmake your life easier.

Special Registers and Scalar and Aggregate Functions

In V5R4, a new set of functions has been added to increase SQL's compatibility with other DB2

implementations.

Special Registers

SQL's new functionality includes four new special registers. Special registers are areas for storing and

retrieving defined values for use within other SQL statements.

The new SESSION_USER and SYSTEM_USER special registers are both used to store and retrieveauthorization information. The SESSION_USER special register is equivalent to the preexisting

USER special register and has been added for increased compatibility with other SQL

implementations. Initially, the value of SESSION_USER will be equal to the SYSTEM_USER specialregister, which contains the user ID used to connect to the current server. The SESSION_USER

special register, however, can be changed at runtime using the SET SESSION AUTHORIZATION

statement.

The CURRENT DEBUG MODE special register controls the level of debugging supported when

procedures are created. Possible values for this special register are DISALLOW, ALLOW, and

DISABLE. A value of DISALLOW indicates that debugging within the Unified Debugger should notbe allowed. This value can be overridden by the SET OPTION DEBUG MODE statement on the

CREATE PROCEDURE statement. A value of ALLOW indicates that the procedure should be

allowed to be debugged within the Unified Debugger. Again, this value can be overridden using the

SET OPTION DEBUG MODE statement. The value of DISABLE indicates that the procedure shouldbe created to not allow debugging from within the Unified Debugger and that the SET OPTION

DEBUG MODE statement will not override this.

The CURRENT DEGREE special register defines the level of I/O or SMP parallel processing to be

used. This value is set using the SET CURRENT DEGREEx statement, wherex is either a value from1 to 32767 or one of several special values. A value of ANY indicates that the system should determine

the level of parallel processing. NONE indicates that no parallel processing should be allowed. A value

of MAX also allows the system to determine the level of parallel processing, but it assumes that all
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active memory in the pool can be used. Finally, a value of IO indicates that no SMP parallelprocessing should be allowed but that any number of IO parallel tasks can occur.

Scalar Functions

V5R4 also contains several new scalar date functions. ADD_MONTHS can be used to obtain a date

that is the result of a given date plus a specified number of months. The first parameter used with thisfunction represents the date to which the months should be added. The value must be a date field, a

timestamp field, or a character field that evaluates to a date. The second parameter defines the number

of months to be added to the date supplied on the first parameter, as shown below:

SELECT ADD_MONTHS('01/29/2006', 1), ADD_MONTHS('01/01/2006', -1)FROM SYSIBM.SYSDUMMY1

The values returned by this statement would be a date value representing the date 2/28/2006 and a datevalue representing the date 12/1/2005. Note that a negative value can be used to effectively subtract

months rather than add them. Also note that if the day portion of the date provided is greater than the

last day of the resulting month, the last day of that month is returned.

The LAST_DAY function accepts a single parameter containing a date value, a timestamp value, or a

character string that evaluates to a date. This function returns the last day of the month for theprovided date, as shown here:

SELECT LAST_DAY('01/15/2006')FROM SYSIBM.SYSDUMMY1

When executed, this statement returns a date value representation of the date 01/31/2006.

The NEXT_DAY function returns the next date associated with a specified day of the week followinga provided date. The first parameter identifies the starting date. The second parameter identifies the

name of day of the week to be returned. Valid values are the full day name ('MONDAY', 'TUESDAY',

etc.) or the proper three-letter abbreviation ('MON', 'TUE', etc.). The example below illustrates thisfunction's use:

SELECT NEXT_DAY('02/08/2006', 'WEDNESDAY')FROM SYSIBM.SYSDUMMY1

When executed, this example returns a date of 2/15/2006, which is the next Wednesday after 2/8/2006.

The VARCHAR_FORMAT function converts a supplied timestamp value or a string representation of

a timestamp value into a VARCHAR representation of the proper timestamp format. The firstparameter supplies the input timestamp value, while the second parameter identifies the format of the

resulting timestamp in VARCHAR format. This value must be specified as 'YYYY-MM-DD

HH24:MI:SS'. In this string, YYYY represents the four-digit year, MM represents the two-digit month,

DD represents the two-digit day, HH24 represents the two-digit hour in 24-hour format, MI representsthe minute portion of the timestamp, and SS represents the seconds portion of the timestamp. Below is


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a sample of this function's use:

SELECT VARCHAR_FORMAT('2006-1-1 9:00:00', ''YYYY-MM-DD HH24:MI:SS')FROM SYSIBM.SYSDUMMY1

When executed, this statement returns the value 2006-01-01 09:00:00. Note that the leading 0's are

inserted in each portion of the timestamp.

The ENCRYPT_TDES function gives the user the ability to encrypt field data within an SQLstatement. Like its predecessor, the ENCRYPT_RC2 function, ENCRYPT_TDES accepts a parameter

containing the string data to be encrypted in BINARY, VARBINARY, CHAR, VARCHAR,

GRAPHIC, VARGRAPHIC, VARCHAR FOR BIT DATA, BLOB, CLOB, or DBCLOB formats. Thefunction also accepts two optional parameters, which are used to supply an encryption password and a

password hint. If the password value is not provided, the data is encrypted using the default encryption

password, which is set using the SET ENCRYPTION PASSWORD statement. Unlike the existingENCRYPT_RC2 function, ENCRYPT_TDES uses the Triple DES encryption algorithm. To populate

a table field with the result of the ENCRYPT_TDES function, the field must be defined as BINARY,

BLOB, CHAR FOR BIT DATA, VARBINARY, or VARCHAR FOR BIT DATA. The length of thefield definition must also take into consideration additional bytes required to store the password data.

This is accomplished by taking the length of the data to be encrypted, adding 16 bytes for the

password, rounding the result up to the next multiple of 8, and finally adding the number of bytes

required for the password hint.

The GENERATE_UNIQUE function generates a unique 13-byte bit character string. This unique

value is generated using a combination of the Universal Time Coordinated (UTC) and the iSeriesserial number. The value returned will be unique each time the function is executed. A column within a

table that contains a GENERATE_UNIQUE value must be defined as CHAR(13) FOR BIT DATA.

The resulting value can also be used along with the TIMESTAMP function to determine the time when

the data was updated.

The RAISE_ERROR function allows a user to return a specified error. The first parameter contains a

five-character string that evaluates to the SQL State associated with the error. The second parametercontains a string with a maximum length of 70 bytes, which contains a diagnostic string related to the

error. This statement is generally used within SQL procedural language. It cannot be used in

circumstances where parameter markers are not allowed, such as from within interactive SQL, withoutusing a CAST specification to define a data type for the function's results. This is because the

RAISE_ERROR's data type is undefined.

Aggregate FunctionsIn addition to these scalar functions, aggregate functions have been added. The STDDEV_SAMPfunction returns the sample standard deviation of a set of numbers. This value is basically the result of

this formula:

SQRT(VAR_SAMP(value))

That is the square root of the sample variance for the set of numbers. The STDDEV_SAMP functionaccepts a single parameter containing the numeric value on which the sample standard deviation is to


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be calculated.

The new VAR_SAMP function, shown above, calculates the sample variance of a set of numbers. As

shown earlier, the single parameter identifies the numeric field on which the VAR_SAMP results are

to be based. Below is the formula used to calculate the sample variance:

(SUM(field ^ 2) - ((SUM(field) ^ 2) / (COUNT(*)))) / (COUNT(*) - 1)

Online Analytical Processing (OLAP)

OLAP functionality has been added to SQL in V5R4. This ability extends the existing aggregate

functionality within SQL by adding ranking and row numbering capabilities. This functionality allows

for greater ability to analyze data using only SQL. The code below shows the syntax used toaccomplish this:

SELECTRANK() OVER(PARTITION BY part defn ORDER BY sort order [ASC, DESC]) AS RANK_VAL,DENSE_RANK() OVER(PARTITION BY part defn ORDER BY sort order [ASC, DESC]) AS DNS_RNK_VAL,

ROW_NUMBER() OVER(PARTITION BY part defn ORDER BY sort order [ASC, DESC]) AS ROW_VALFROM table name

The RANK and DENSE_RANK specifications allow you to retrieve a ranking within a defined group

of fields for the current record. The field definition is based on the list of fields defined on the ORDERBY clause. The PARTITION BY clause can also be included to define partitioning of the ranking data.

The statement below gives an example of this:

SELECT DIVISION, CUSTOMER, SALES$,RANK() OVER(PARTITION BY DIVISION ORDER BY SALES$ DESC) AS SALES_RANKFROM SALES_DATAORDER BY DIVISION, RANK() OVER(PARTITION BY DIVISION ORDER BY SALES$ DESC)

In this example, the data will be ranked by sales dollars within each division. The numbering returnedwill represent the ranking within the PARTITION BY value specified. Note that we've used the

RANK() specification again within the ORDER BY clause for our SELECT statement to indicate that

the result set should be sorted by the sales dollars. The way that ranking is determined when theORDER BY values are identical depends on whether you use RANK or DENSE_RANK. While

RANK will assign identical values the same rank, it also increments the "rank counter," meaning that

if the top five records all have the same ORDER BY value, they will all appear as the number 1ranking, but the sixth record will have a ranking of 6. If DENSE_RANK is used, the first five records

will still have a ranking of 1, but the next record will have a ranking of 2.

The ROW_NUMBER specification is similar to the RANK specification. It returns the sequential row

number within the defined partition, based on the ORDER BY clause. ROW_NUMBER, however,does not group like values as the RANK and DENSE_RANK specifications do. Below is a sample of

using ROW_NUMBER:

SELECT ROW_NUMBER() OVER (ORDER BY DEPT, LNAME ) AS ROW_N, LNAME, SALRY$FROM PAYROLLORDER BY DEPT, LNAME

This example displays a row number within a DEPT group based on the value of the LNAME field.

The ASC and DESC modifiers can be added to the ORDER BY clause to identify ascending or

descending order. The optional NULLS FIRST and NULLS LAST values can be specified to force


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any null values to the beginning or end of the result set. The ORDER OF clause can be used in placeof the ORDER BY clause to identify that the data set should be ordered using the sort order of the

table specified.

SELECT ROW_NUMBER() OVER (ORDER OF PAYROLL) AS ROW_N, LNAME, SALRY$FROM PAYROLLORDER BY DEPT, LNAME

In this example, the value PAYROLL identifies that the order of our data should be the same sort orderdefined on the PAYROLL table.

Free-Form ILE RPG Embedded SQL

If you're an "embedded SQL junkie" like I am, this is the language enhancement you've been waiting

for. Prior to V5R4, in order to execute an embedded SQL statement from a free-form program, youhad to exit from free-form using the/END FREEcompiler directive and then enter embedded SQL

using the/EXEC SQL compiler directive. In V5R4, IBM has simplified the process and in turn made

embedding SQL into an RPG program even more seamless. Below is a snippet of code showing how a

free-form ILE RPG program with embedded SQL would have to be coded priorto V5R4:

C/FreeSQL_Str = 'SELECT NAME FROM CUSTOMERS , ' +

' WHERE STATE= ? AND ACTBAL>0 '; /END-FREEC/EXEC SQL

C+ PREPARE SQL_STMT FROM :SQL_Str

C/END-EXEC

C/EXEC SQL

C+ DECLARE CUST_Crsr CURSOR FOR SQL_STMTC/END-EXEC

C/EXEC SQL

C+ OPEN CUST_Crsr USING :STCD C/END-EXECC/EXEC SQL

C+ FETCH CUST_Crsr INTO :CUSTNAME C/END-EXECC/Free

DoW SQLCOD 100 and SQLCOD >= 0;

Write PRINTP1; EndDo; /End Free

You'll notice that each instance of switching from free-form to SQL requires at least two additional

lines of code, not to mention the fact that we need to use the /EXEC SQL and /END-EXEC directives

for each SQL statement we want to execute. This means that a single line of SQL takes up three lines


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of code. In V5R4, IBM has rectified this problem. The code below shows how the previous examplecan be coded in V5R4:

C/FreeSQL_Str = 'SELECT NAME FROM CUSTOMERS , ' +

' WHERE STATE= ? AND ACTBAL>0 ';

EXEC SQL PREPARE SQL_STMT FROM :SQL_Str;EXEC SQL DECLARE CUST_Crsr CURSOR FOR SQL_STMT;EXEC SQL OPEN CUST_Crsr USING :STCD; EXEC SQL FETCH CUST_Crsr INTO :CUSTNAME; DoW SQLCOD 100 and SQLCOD >= 0;Write PRINTP1; EndDo; /End Free

As you can see, this much simpler method of coding embedded SQL not only reduces the number of

code lines required, but actually makes the code much easier to read. Once again, this indicates IBM'scommitment to the further use of SQL as well as the continued development of the RPG language.

DB2 UDB and SQL

With the continued evolution of SQL on the iSeries, IBM has shown its eagerness to keep DB2 UDB

for the iSeries in line not only with versions of DB2 for other platforms, but also with other

implementations of SQL. One can only wonder what goodies they'll have for us in the nextrelease.

Mike Faust is an Application Programmer for Fidelity Integrated Financial Solutions in

Maitland, Florida. Mike is also the author of the books The iSeries and AS/400 Programmer'sGuide to Cool ThingsandActive Server Pages Primerand SQL Built-in Functions andStored Procedures. You can contact Mike at [email protected].
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