SQL/MX 2.x Query Guide (H06.04+, J06.03+)

HP NonStop SQL/MX Query Guide—540437-005
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Compiling and Executing a Query
Use the information in this section to understand how your queries are compiled and
executed.
•
How the Compiler Works on page 1-2
•
How the Executor Processes the Plan on page 1-19
Overview
At the highest level, compiling and executing an SQL query with NonStop SQL/MX
consists of two basic steps.
1. The SQL/MX compiler processes the query and produces a query execution plan.
2. The SQL executor processes the execution plan and produces the query result.
These actions can influence query optimization, as shown in Step 1:
•
Forcing plans with the CONTROL QUERY SHAPE statement
•
Changing default settings with the CONTROL QUERY DEFAULTS statement
•
Keeping statistics current with the UPDATE STATISTICS statement
•
Changing system default settings in the SYSTEM_DEFAULTS table
VST110.vsd
System
Defaults
Control
Query
Defaults
Control
Query
Shape
Statistics
(histograms)
Metadata
QUERY
QUERY
Query
Execution Plan
Query
Execution Plan
SQL/MX COMPILER
Query
Execution Plan
SQL/MX EXECUTOR
VST120.vsd
Result