1. A – Pre Join Indexes

2. Types of Joins Ad-hoc joins Join index Joined at query time
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
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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
Nested loop: Takes a row from the larger table of the join and compares it to each row of the smaller table
You want the rows from the smaller side of the join to stay in memory
Hash: Similar to nested loop, except the smaller side is “hashed” into an in-memory table with a hashing function applied to the join keys
Requires fewer comparisons than a nested loop, but adds the cost of computing the hash key for each row on both sides of the join
Sort/merge: Sorts the rows on both sides and then compares the rows
Sort/merge push down: Bloom-filter based semijoin that significantly reduces the number of rows projected and the number of rows to be sorted
Nested loop push down: IQ turns the keys of the smaller side of the join into an IN list on the large table
Hash push down: Combination of a hash join and ASIQ’s special index processing
Cartesian nested loop: A variation of the nested loop join. A many-to-many or Cartesian join will produce a row for every combination of rows from both Cartesian nested loop sides.
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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
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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
For performance reasons, a ratio of less than 5 to 1 is preferred
The space required for a join index can be HUGE
Join indexes can take a LONG time to build
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6. Ad-Hoc Joins Versus Join Indexes
Join indexes can involve multiple tables and are subject to certain rules
Even if extra build time is available and additional disk space is not an issue, join indexes cannot be created in all cases
Synchronizing is discussed in detail later in the module
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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...
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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
...)
The example in this module joins customer and product tables. You would also need to create the product table as part of step 1.
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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)
ONE >>MANY: One row in one table potentially matches with one or more rows in another table
MANY>>ONE: One or many rows in one table potentially match with one row in another table
ONE >>ONE: One row in the first table potentially matches with one row in the second table
If the join relationship specified is incorrect, the extra rows are discarded and not included in the join index
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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
In this example, Table C is the “top table”
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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
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12. Entity-Relationship Diagram
This example is used throughout this module
In this entity-relationship diagram, a customer can have one or more orders
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13. Join Hierarchy with the Top Table
order becomes the top table because it is on the MANY side of the relationship
order table is the “Top Table”
Continued …
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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 ...
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15. Step 3: Create the Indexes
Create the column indexes for the tables being joined
Columns involved in joins must have an HG or LF index
Example:
CREATE HG index customer_id_HG on
customer(customer_id);
CREATE LF index cust_type_LF on
customer(cust_type);
...
To determine the index types for each column, see Module 5, “ASIQ Index Types and Data Types”
To create indexes on each column, see Module 6, “Creating Tables and Indexes”
Remember to create all the indexes for the customer and order tables
Indexes can be created either using the CREATE INDEX command or using Sybase Central
Continued …
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16. Step 4: Load Data Continued … Load the data into the tables Example:
Can use LOAD TABLE or INSERT command
See Modules 9, 10, and 11 on data loading
Example:
LOAD TABLE customer
(customer_id '|'
... )
FROM ... ;
You need to load or insert data into the order table also
Continued …
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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...
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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
join-clause
[ ( ] join-expression join-type join-expression
[ on search-condition ] [ ) ]
join-expression
{ table-name | join-clause }
join-type
[ NATURAL ] FULL [ OUTER ] JOIN
You need to code the join index correctly. ASIQ assumes the sub-tree on the left is the ’one’, while the join expression on the right is the ’many’ side. If you specify incorrectly, the create will return an error.
Another example and further explanation follow later in this module
Continued …
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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 …
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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
Foreign and primary keys must be defined during the CREATE TABLE operation for customer and order tables in the following Key join example:
CREATE JOIN INDEX key_customer_order_join
FOR customer FULL OUTER JOIN order
Continued …
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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
You can create a join index in Sybase Central. Sybase Central
See Chapter 4 of the Adaptive Server IQ Administration and Performance Guide
Continued …
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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...
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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)
If you complete step 5 (CREATE JOIN INDEX) before step 4 (LOAD TABLE or INSERT), you do not have to synchronize the data for the initial setup
Make sure you have plenty of space in your IQ Temporary Store. The synchronize process uses the IQ Tempory Store.
Continued …
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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
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25. Multiple-Table Join Example
Join Hierarchy:
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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
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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
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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
Default values:
Relationship: one-to-many
IQ page size: 64KB
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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
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30. Dropping a Join Index Syntax: Example:
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
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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
Insert to include:
LOAD TABLE
INSERT FROM SELECT
INSERT VALUES
Prior to version , update was not allowed on joined indexes
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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 …
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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
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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.
May 6, 2019