Crystal Reports - The Power and Possibilities of SQL Expressions

The Power and Possibilities of
SQL Expressions
Kurt Reinhardt, Crystal Advantage

Topics

What is a SQL Expression?
SQL Expressions Vs. Formulas
SQL Expression Samples
When to use a SQL Expression
Troubleshooting SQL Expression errors
Q&A

Slide 3 Copyright © 2006 Business Objects S.A. All rights reserved.

SQL Expressions allow one to:
Eliminate
unnecessary
subeports!
Increase
performance!
Optimize efficiency!
Reduce subreport
instances!



Everybody wants to know!
 Knowledge base article c2016183 – What is the intended use of ‘SQL
Expression Fields’? was one of the most visited articles for July 2006!
Similar to Formulas but written in SQL
 Generally used against SQL-based databases
 Will be disabled if your database isn’t compatible
SQL Concepts
 Subqueries / Subselects
 Correlated Vs. Uncorrelated


What is a SQL Expression? 1/2
Correlated Subquery
Fields from the Outer Query are passed to the Subquery:

SELECT
A.REPAIR_ORDER_ID,
A.REPAIR_FACILITY_CD,
NVL((SELECT
DECODE(X.FINDING_CONDITION_TXT,’TRUE’,’Y’,’N’)
FROM
RECORDED_FINDING_CONDITION X
WHERE
X.REPAIR_ORDER_ID = A.REPAIR_ORDER_ID
AND X.REPAIR_FACILITY_CD = A.REPAIR_FACILITY_CD
AND X.FINDING_QUESTION_ID = ‘smart_scope’
AND X. FINDING_CONDITION_ID = ‘TRUE’
),’N’) SMART_SCOPE
FROM
FINDING_HEADER A


What is a SQL Expression? 2/2
Uncorrelated Subquery
The Subquery doesn’t relate to any fields:

SELECT
C."Customer ID",
C."Customer Name",
(
SELECT
SUM("Order Amount")
FROM
ORDERS
) 'Total Orders'
FROM
CUSTOMER C
ORDER BY
C."Customer ID"



General Guidelines to Consider
 Intended to be used against SQL-based databases
 Can be used against certain PC-based databases
 Can’t access Formula or Parameter fields
 Available functions are based on your db and method of connectivity
 SQL Expressions are always added as fields in the SELECT clause
 SQL Expressions must return a single, distinct value


Topics

Q&A



Multi-pass Reporting
 SQL Expressions - processed on the database during Pass #1
 Formulas - many processed on the client during Pass #2
Database Considerations
 SQL Expressions – used against SQL-based databases
 SQL Expressions – must be used against tables / views
 Formulas - can be used against any data source
Report Design
 SQL Expressions – only reference database fields
 Formulas - can reference all other Crystal Reports field elements


Topics

Q&A



Using SQL Expressions to prequery subreport data:
 Customer Report – grouped by Customer
 Has a subreport in the Group Footer
 The subreports don’t always have data, but still run every time
 Report performance suffers
 The database and network are impacted


SQL Expression Samples 1/7
Prequery - Two customers, one with a blank subreport


Prequery - 322 subreport instances!


Prequery - Create a SQL Expression


Prequery - Check SQL Expression for NULLs with Formula


Prequery - Conditionally suppress subreport


Prequery - Conditionally suppress report section


Prequery - Only 196 instances in 1 minute 15 seconds!
That’s a 44% performance increase!



Using SQL Expressions to eliminate subreports:
 Report has a subreport that returns a single aggregate value
 A Shared Variable is used to pass the value back to the main report
 Main report uses the value in calculations
 Performance is not optimal due to subreport
 Report is overly complex


Aggregate Value – Create SQL Expression


Aggregate Value – Use SQL Expression in calculations



Using SQL Expressions to optimize selection criteria:
 Listing of Practitioners with Missing or Incomplete SSNs
 Report uses Formulas in the Record Selection Criteria
 The Formula isn’t passed to the database for processing
 Performance suffers


Optimization – Formulas in the Record Selection Criteria


Optimization – The Formulas aren’t passed to the database
Database|Show SQL Query
 Notice, there is no WHERE clause
 All possible records will be returned and filtered out on the Client
Example of code below
SELECT "ENTITY"."ENTITY", "PRACENT"."PRACID",
"PRACENT"."NAME", "PRAC"."SSNUM",
"ENTITY"."DESCRIPTION"
FROM ("ENTITY" "ENTITY" INNER JOIN "PRACENT"
"PRACENT" ON "ENTITY"."ENTITY"="PRACENT"."ENTITY")
INNER JOIN "PRAC" "PRAC" ON
"PRACENT"."PRACNO"="PRAC"."PRACNO"
ORDER BY "ENTITY"."ENTITY", "PRACENT"."NAME"


Optimization – Create SQL Expressions


Optimization – Substitute SQL Expressions for Formulas


Optimization –SQL Expressions ARE passed to the database!
 WHERE clause is present
 Only records that meet the criteria will be returned
…
WHERE ("PRAC"."SSNUM" IS NULL OR ({fn
RTRIM(PRAC."SSNUM")}
)='' OR ({fn LENGTH(PRAC."SSNUM")}
)<>11)
ORDER BY "ENTITY"."ENTITY", "PRACENT"."NAME"



Using SQL Expressions to filter against aggregates:
 Most Recent Orders by Customer
 The report lists all customers and their most recent order only
 Traditional Method 1: using a subreport to find the Max Order Date
 Traditional Method 2: suppressing all records via Group Selection
 Report is inefficient
 Performance suffers


Most Recent – Create a SQL Expression


Most Recent – Apply SQL Expression to Record Selection


Most Recent – The filter is applied on the database!
 WHERE clause is present
 Only records that meet the criteria will be returned
…
WHERE "Orders"."Order Date"=((
SELECT
MAX("ORDER DATE")
FROM
ORDERS
WHERE
"CUSTOMER ID" = "Customer"."Customer ID"
))
…

Topics

Q&A


When to use SQL Expressions

Generally in table-based reports
 Creating Views or Stored Procedures may not be an option
 Many companies limit database access for report writers
 The database may be proprietary
 It may be simpler to create a SQL Expression than to modify a View
 Stored Procedures and SQL Commands may limit functionality


Topics

Q&A


Troubleshooting SQL Expression Errors

Only attempt to return a single, distinct value
Use the most recent Service Pack
 Especially important for Crystal Reports 7 – Crystal Reports 8.5
Some keywords are prohibited
Try encapsulating your code in parentheses
 Required by some databases such as MS SQL Server
Test the code in an analyzer first
Copy the code from the analyzer


Q&A

Questions
 Kurt Reinhardt, Crystal Advantage
 I will repeat questions to ensure everyone can hear
Contact information
 Email: kreinhardt@crystaladvantage.com


Crystal Reports - The Power and Possibilities of SQL Expressions

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