Query processing, Storage, Indexing in SQL

Database Management
Systems



Unit-6
Query Processing
and Optimization

, Topics to be covered
• Overview (Query Processing)
• Measures of query cost
• Selection operation
• Evaluation of expressions
• Query optimization
• Transformation of relational expressions
• Sorting and join



Unit – 5: Query Processing & Optimization 2

, Explain Query Processing.
 Query Processing is the activity performed in extracting data from
the database.
 It is a process of transforming a high-level query (such as SQL) in
to low level language.
 In query processing, it takes various steps for fetching the data
from the database.

 The steps involved are:
1. Parsing and translation
2. Optimization
3. Evaluation


Unit – 5: Query Processing & Optimization 3

, Steps in Query Processing
The Scanner verifies Translator translates the
attribute name and relation query into its internal
name and The Parser form (relational algebra)
checks the syntax of query
Scanner, Relational algebra
Query Parser and expression
translator
Choose best execution plan
Optimizer
Execute the query-evaluation
plan and returns output
Evaluation
Query output Execution plan
engine


Database Catalog
Data Statistics about Data

Unit – 5: Query Processing & Optimization 4