A – Pre Join Indexes

1. A – Pre Join Indexes

2. Types of Joins • Ad-hoc joins • Joined at query time • Join index • An internal structure that relates table columns • Represents two or more tables, including inner, left outer, and right outer rows • May provide better performance than ad-hoc joins • Requires additional disk space and time to create

3. Ad-Hoc Joins • A join merges rows from two tables into a result table • Six types of ad-hoc join algorithms • Nested loop • Hash • Sort/Merge • Sort/Merger push down • Nested loop push down • Hash push down • Cartesian nested loop

4. When to Use Ad-Hoc Joins • Instead of Join Indexes • Always try ad-hoc joins first before creating join indexes • If the ratio of data in join tables is higher than 10 to 1 • For example, lookup tables • Ad-hoc joins recommended due to data explosion • For self-joins • For many-to-many relationships

5. When to Create a Join Index • After trying ad-hoc queries • If certain tables are typically joined together in queries • There is adequate disk space • Fairly static tables • Ratio of data in join index is less than 10 to 1 • This limit is due to high disk overload • Recommend a ratio of less than 5 to 1 for performance reasons

6. Ad-Hoc Joins Versus Join Indexes • Join indexes can involve multiple tables and are subject to certain rules

7. Creating a Join Index • Step Overview • Step 1: Create the tables involved in the join index • CREATE TABLE... • Step 2: Define the relationships • Step 3: Create the indexes for the tables being joined • CREATE INDEX... • Step 4: Load the data into the tables • LOAD TABLE... or INSERT... • Step 5: Create the join index • CREATE JOIN INDEX... • Step 6: Synchronize join index, if required • SYNCHRONIZE JOIN INDEX...

8. Step 1: Create Tables • Create the tables involved in the join index • CREATE TABLE command • Sybase Central • See Module 7, “Creating Tables and Indexes” • Example: • CREATE TABLE customer • (customer_id int not null • ,cust_type char(4) null • ,organization char(30) null • ...)

9. Step 2: Define the Relationships • Must determine the relationships between each pair of tables • Types • One-to-many (ONE>>MANY) • Many-to-one (MANY>>ONE) • One-to-one (ONE>>ONE)

10. Join Hierarchy • All IQ join relationships must have a join hierarchy • A tree that illustrates how all the tables in a join are connected • Determine the top table, which is always on the MANY side • Rules • A table can occur only once • A table can have only one arrow leaving it • All tables must be connected • An arrowhead is the MANY side of a relationship

11. Types of Join Hierarchies • Linear joins • Each table is related to the table above it, until you reach the top table • Each pair of tables represents a one-to-many relationship • Star joins • Each table is related to one table in the middle • The table in the middle represents the MANY side, sometimes called the fact table • The ONE tables are called dimension tables • You can create join indexes or have ad-hoc joins for both linear and star joins

12. Entity-Relationship Diagram • This example is used throughout this module

13. Join Hierarchy with the Top Table • order table is the “Top Table” Continued …

14. Creating a Join Index • Step Overview • Step 1: Create the tables involved in the join index • CREATE TABLE... • Step 2: Define the relationships • Step 3: Create the indexes for the tables being joined • CREATE INDEX... • Step 4: Load the data into the tables • LOAD TABLE... or INSERT... • Step 5: Create the join index • CREATE JOIN INDEX... • Step 6: Synchronize the join index, if required • SYNCHRONIZE JOIN INDEX ...

15. Step 3: Create the Indexes • Create the column indexes for the tables being joined • Columns involved in joins must have an HG or LFindex • Example: • CREATE HG index customer_id_HG on • customer(customer_id); • CREATE LF index cust_type_LF on • customer(cust_type); • ... Continued …

16. Step 4: Load Data • Load the data into the tables • Can use LOAD TABLE or INSERT command • See Modules 9, 10, and 11 on data loading • Example: • LOAD TABLE customer • (customer_id '|' • ... • ) • FROM ... • ; Continued …

17. Creating a Join Index • Step Overview • Step 1: Create the tables involved in the join index • CREATE TABLE... • Step 2: Define the relationships • Step 3: Create the indexes for the tables being joined • CREATE INDEX... • Step 4: Load the data into the tables • LOAD TABLE... or INSERT... • Step 5: Create the join index • CREATE JOIN INDEX... • Step 6: Synchronize join index, if required • SYNCHRONIZE JOIN INDEX...

18. Step 5: Create the Join Index • Must be DBA or the table owner and have RESOURCE authority to CREATE JOIN INDEX • Syntax: • CREATE JOIN INDEX join-index-name • FOR join-clause • Example: • CREATE JOIN INDEX customer_order_join • FOR customer FULL OUTER JOIN order • ON customer.customer_id = order.customer_id Continued …

19. Step 5: Create the Join Index • Specifying the Join Type • Join type is always FULL OUTER; OUTER keyword is optional • If you are joining equivalent columns with the same names, you specify NATURAL JOIN • If you are joining columns based on keys, you must have specified FOREIGN and PRIMARY keys • Use the ON clause to join equivalent values in two tables Continued …

20. Step 5: Create the Join Index • Same example (natural join): • CREATE JOIN INDEX nat_customer_order_join • FOR customer NATURAL FULL OUTER JOIN order • Join column names must be the same in the tables being joined Continued …

21. Step 5: Create the Join Index • Results: • When you create a join index, a message in the log appears: • : Join Index 'customer_order_join' • created from the following join relations. • : Table Name Relationship • :-------------------------------------------- • :1. customer joined to order One >> Many • :The ultimate/top table is order • :-------------------------------------------- Continued …

22. Creating a Join Index • Step Overview • Step 1: Create the tables involved in the join index • CREATE TABLE... • Step 2: Define the relationships • Step 3: Create the indexes for the tables being joined • CREATE INDEX... • Step 4: Load the data into the tables • LOAD TABLE... or INSERT... • Step 5: Create the join index • CREATE JOIN INDEX... • Step 6: Synchronize join index, if required • SYNCHRONIZE JOIN INDEX...

23. Step 6: Synchronize Join Indexes • This step ensures that the data is loaded in the correct order for the join • It automatically occurs when: • You create the join index • Changes are made to the top table of the join hierarchy • Otherwise, must be manually performed, which can be time-consuming • Schedule during off-peak hours • Synchronize after entire set of inserts and deletes (do not do after every insert or delete) Continued …

24. Step 6: Synchronize Join Indexes • Syntax: • SYNCHRONIZE JOIN INDEX [ join-index-name [, join-index-name] • If you omit the index name, IQ synchronizes all join indexes • Because this process is so time consuming, it is best to specify joins and schedule them individually • Example: • SYNCHRONIZE JOIN INDEX customer_order_join

25. Join Hierarchy: Multiple-Table Join Example

26. To Create the Join Index • CREATE JOIN INDEX cust_prod_order_join • FOR customer • FULL OUTER JOIN order • ON customer.customer_id = order.customer_id • FULL OUTER JOIN product • ON order.product_id = product.product_id • If no key definitions exist a ONE>>MANY is assumed left to right

27. Rules for Join Indexes • Conditions and Restrictions • You must be Database Administrator or table owner • You can combine steps 1 and 2 by defining relationships when you create the table (define keys) • You need to synchronize after additional inserts/deletes unless you have updated the top table • This approach is not recommended for data ratios greater than 10 to 1 (less than 5 to 1 may provide more optimal performance) • Join indexes cannot be created on many-to-many relationships

28. Estimating Join Index Size • Stored procedure syntax: • sp_iqestjoin table1, #ofrows, table2, #ofrows [, relation] [, iq_page_size] • Estimates the space needed to create join indexes • Example: • sp_iqestjoin customer, 10000, order, 30000 • You must run this procedure for each pair of tables being joined

29. Actual Join Index Size • Stored procedure syntax: • sp_iqjoinindexsize (join-index-name) • Returns the total size of the index in bytes • Example: • sp_iqjoinindexsize customer_order_join

30. Dropping a Join Index • Syntax: • DROP JOIN INDEX join-index-name • Example: • DROP JOIN INDEX customer_order_join • You must first drop the join index before dropping an underlying table

31. Data Modification in a Join Index • Always insert, update, or delete from the underlying tables, not from the join index • You cannot do partial-width inserts to tables that participate in a join index • Drop the join index, do the partial-width insert, and then recreate the join index • Do not forget to synchronize

32. How Join Indexes Are Used • The SELECT statement determines whether a join index will be used • Determined by the FROM and WHERE clauses • Do not need to specify the join index name in a query • IQ can use the same join index to resolve a query that involves the full join relationship or a query that involves a contiguous subset Continued …

33. How Join Indexes Are Used • Queries that can be resolved • Entire relationship • A to D • B to D • D to F • C to E • E to F • C to E to F • Example of a query that cannot be resolved using the join index: • E to D

34. Summary • Try using ad-hoc joins first. • Create a join index if: • Ratio of data in join tables is less than 10 to 1 (recommend less than 5 to 1). • No many-to-many relationships. • Same tables are frequently joined together in queries. • There is adequate disk space.