Database access is critical to any project. It's easy to low down the performance with heavy queries, or using multiple queries to get a simple information. Or even that initial query that cascade to dozens of others using programming... And everything gets worse if the database has lots of data or a poorly designed query! Each query has a high cost to your application. It's possible to solve this kind of problems using CTE (Common Table Expression). This powerful resource is available on most of the relational database but isn't well known by developers. Deal with a significant amount of data with simple maintenance and drastically increase your database performance!

1. Dramatically increase your database's
performance using hierarchical and
recursive queries
Dani Monteiro
@DaniMonteiroDBA
Rodrigo Moutinho
@rcmoutinho

2. • Hacking your query
• Know about the available resources
• Hierarchical queries
• Recursive queries
Agenda

3. • Tables and relationships
• Available indexes
• Data volume on each queried table
Hacking your query

4. Hacking your query

5. • ERP TOTVS
• Sports T-shirt Factory
• What do I have to release in my stock?
• Daily process of more than two hours (after one click)
Real Example

6. • Subqueries
• Views
• Materialized Views
• Functions
Available Resources

7. • Request any database process
• To create a query
• To create and use a database feature (views, functions, ...)
Permission Levels

8. SELECT
SC5.C5_NUM AS PED,
SC5.C5_VEND1 AS REPRES,
SA1.A1_NOME AS NOME,
(SELECT SUM((C6_QTDVEN - C6_QTDENT))
FROM SC6010 C6, SC9010 C9 WHERE ... [10 condições] ) AS QTDFAL,
(SELECT SUM((C6_QTDVEN - C6_QTDENT) * C6_PRCVEN)
FROM SC6010 C6, SC9010 C9 WHERE ... [10 condições] ) AS VALFAL,
(SELECT SUM (((C6_QTDVEN - C6_QTDENT) * C6_PRCVEN) - (C6_XQTD05 * C6_PRCVEN))
FROM SC6010 C6, SC9010 C9 WHERE ... [10 condições] ) AS VALOR,
SE4.E4_COND AS COND,
SC5.C5_OBSPED AS OBS,
SC5.C5_PREVIST as PREV,
SC5.C5_XST05 AS ST,
SC5.C5_XFRET AS FRET,
(SELECT SUM(C6_VALOR)
FROM SC6010 C6, SC9010 C9 WHERE ... [9 condições] ) AS TOT
FROM SC5010 SC5, SC6010 SC6, SC9010 SC9, SA1010 SA1, SF4010 SF4, SE4010 SE4
WHERE ... [29 condições]
GROUP BY SC5.C5_NUM, SC5.C5_VEND1, SA1.A1_NOME, SE4.E4_COND,
SC5.C5_OBSPED, SC5.C5_PREVIST, SC5.C5_XST05, SC5.C5_XFRET
ORDER BY SA1.A1_NOME
Subqueries

9. Subqueries
Quantidade
Faltante
SC6 - Item
Pedido Venda
SC9 - Item
Pedido Venda
Liberado
SUM SELECT

10. Subqueries
QTDFAL
SC6
SC9
SUM
VALFAL
SC6
SC9
VALOR
SC6
SC9
TOTAL
SC6
SC9
SUM
SUM
SUM
SELECT
SELECT
SELECT
SELECT
SELECT

11. Common Table Expression
WITH NICKNAME_1 AS (
SELECT ... FROM TABLE_1 ...
), NICKNAME_2 AS (
SELECT ... FROM NICKNAME_1 INNER JOIN TABLE_2 ...
)
SELECT ... FROM NICKNAME_1 INNER JOIN NICKNAME_2 ...
WHERE ...
GROUP BY ...
ORDER BY ...

12. Hierarchical Queries
• Reuse queries as a temporary result
WITH TABLE_PEDIDO AS (
SELECT ...
), TABLE_QUANTIDADE AS (
SELECT ...
), TABLE_ITENS_C6 AS (
SELECT ... FROM TABLE_QUANTIDADE ...
)
SELECT ...
FROM TABLE_PEDIDO AS T_PEDIDO, TABLE_ITENS_C6 AS T_ITENS_C6, ...
WHERE ...
ORDER BY ...

13. Better Performance
), TABLE_QUANTIDADE AS (
SELECT
C6_NUM AS C6NUM, C6_QTDVEN AS C6QTDVEN, C6_QTDENT AS C6QTDENT,
C6_PRCVEN AS C6PRCVEN, C6_XQTD05 AS C6XQTD05, C6_VALOR AS C6VALOR,
C6_XFLAG AS C6XFLAG, C6_LOCAL AS C6LOCAL, C6_TES AS C6TES
FROM SC6010 C6, SC9010 C9
WHERE ... [11 condições]
), TABLE_ITENS_C6 AS (
SELECT
C6NUM AS NUM,
C6TES AS C6TES,
SUM( (C6QTDVEN-C6QTDENT) ) AS QTDFAL,
SUM( (C6QTDVEN-C6QTDENT) * C6PRCVEN ) AS VALFAL,
SUM( ( (C6QTDVEN-C6QTDENT) * C6PRCVEN) - (C6XQTD05 * C6PRCVEN) ) AS VALOR,
SUM(C6VALOR) AS TOT
FROM TABLE_QUANTIDADE
GROUP BY C6NUM, C6TES
)

14. Better Performance
Resultado
Pedidos de
Venda
Somatório
Quantidades
Quantidades
Item Pedidos de
Venda

15. Readability
WITH TABLE_PEDIDO AS (
SELECT ... FROM SC5010 SC5 WHERE ...
), TABLE_QUANTIDADE AS (
SELECT ... FROM SC6010 C6, SC9010 C9 WHERE ...
), TABLE_ITENS_C6 AS (
SELECT ... FROM TABLE_QUANTIDADE ...
)
SELECT DISTINCT T_PEDIDO.PED AS PED, T_PEDIDO.REPRES AS REPRES,
SA1.A1_NOME AS NOME, T_ITENS_C6.QTDFAL AS QTDFAL, ...
FROM TABLE_PEDIDO AS T_PEDIDO, TABLE_ITENS_C6 AS T_ITENS_C6, ...
WHERE T_ITENS_C6.NUM = T_PEDIDO.PED
AND SA1.A1_FILIAL = ' '
...

16. Readability
WITH TABLE_PEDIDO AS (
SELECT
SC5.C5_NUM AS PED,
SC5.C5_VEND1 AS REPRES,
SC5.C5_OBSPED AS OBS,
...
FROM SC5010 SC5
WHERE ... [6 condições]
), TABLE_QUANTIDADE AS (

17. Readability
), TABLE_QUANTIDADE AS (
SELECT
C6_NUM AS C6NUM,
C6_QTDVEN AS C6QTDVEN,
C6_QTDENT AS C6QTDENT,
...
FROM SC6010 C6, SC9010 C9
WHERE ... [11 condições]
), TABLE_ITENS_C6 AS (

18. Readability
), TABLE_ITENS_C6 AS (
SELECT
C6NUM AS NUM,
C6TES AS C6TES,
SUM( (C6QTDVEN-C6QTDENT) ) AS QTDFAL,
SUM( (C6QTDVEN-C6QTDENT) * C6PRCVEN ) AS VALFAL,
SUM( ( (C6QTDVEN-C6QTDENT) * C6PRCVEN) - (C6XQTD05 * C6PRCVEN) ) AS VALOR,
SUM(C6VALOR) AS TOT
FROM TABLE_QUANTIDADE
GROUP BY C6NUM, C6TES
)

19. Readability
SELECT DISTINCT
T_PEDIDO.PED AS PED,
T_PEDIDO.REPRES AS REPRES,
SA1.A1_NOME AS NOME,
T_ITENS_C6.QTDFAL AS QTDFAL,
...
FROM
TABLE_PEDIDO AS T_PEDIDO,
TABLE_ITENS_C6 AS T_ITENS_C6,
SA1010 AS SA1,
SF4010 AS SF4,
SE4010 AS SE4
WHERE ... [11 condições]
ORDER BY SA1.A1_NOME

20. • Reuse query result
• Hierarchical structures
Recursive Queries

21. • Shows the result by levels
• What are the "root" records
• Then the "children"
• Then, "children" of the "children”...
Recursive Queries

22. Example... A menu
Fonte das imagens: https://blogs.msdn.microsoft.com/fcatae/2010/11/10/query-recursiva/

23. What about the code?
WITH RECURSIVE cteMenuNivel(id,Nome,Nivel,NomeCompleto)
AS (-- Ancora
SELECT id,Nome,1 AS 'Nivel',CAST(Nome AS VARCHAR(255)) AS 'NomeCompleto'
FROM tbMenu WHERE idPai IS NULL
UNION ALL
-- Parte RECURSIVA
SELECT
m.id,m.Nome,c.Nivel + 1 AS 'Nivel',
CAST((c.NomeCompleto + '/' + m.Nome) AS VARCHAR(255)) 'NomeCompleto'
FROM tbMenu m INNER JOIN cteMenuNivel c ON m.idPai = c.id)
SELECT Nivel,NomeCompleto FROM cteMenuNivel;

24. • Easier
• Depending on the number of levels
the performance is better
Why CTE?

25. Rodrigo Moutinho
@rcmoutinho
Dani Monteiro
@DaniMonteiroDBA
http://bit.ly/cte-example