Crystal Reports - The Power and Possibilities of SQL Expressions

The Power and Possibilities of SQL Expressions

The Power and Possibilities of SQL Expressions

Kurt Reinhardt, Crystal Advantage

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

What is a SQL Expression?

SQL Expressions Vs. Formulas

SQL Expression Samples

When to use a SQL Expression

Troubleshooting SQL Expression errors

Q&A

Topics


Eliminate unnecessary subeports!

Increase performance!

Optimize efficiency!

Reduce subreport instances!


SQL Expressions allow one to:


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



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_SCOPEFROM FINDING_HEADER A

What is a SQL Expression? 1/2

Correlated 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 CORDER BY C."Customer ID"

What is a SQL Expression? 2/2

Uncorrelated Subquery


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








Q&A

Topics



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







Q&A

Topics



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!

Database|Show SQL Query WHERE clause is present Only records that meet the criteria will be returned

Example of code below …

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!

Database|Show SQL Query WHERE clause is present Only records that meet the criteria will be returned

Example of code below …

WHERE "Orders"."Order Date"=((

SELECT

MAX("ORDER DATE")

FROM

ORDERS

WHERE

"CUSTOMER ID" = "Customer"."Customer ID"

))

…







Q&A

Topics


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







Q&A

Topics


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


Questions Kurt Reinhardt, Crystal Advantage I will repeat questions to ensure everyone can hear

Contact information Email: [email protected]

Q&A

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Crystal Reports - The Power and Possibilities of SQL Expressions