1. The Query Compiler. 16. 1 Parsing and Preprocessing. Meghna Jain(205)
The Query Compiler Parsing and Preprocessing Meghna Jain(205) Dr. T. Y. Lin

2. Presentation Outline 16.1 Parsing and Preprocessing
Syntax Analysis and Parse Tree
A Grammar for Simple Subset of SQL
The Preprocessor
Processing Queries Involving Views

3. Query compilation is divided into three steps
1. Parsing: Parse SQL query into parser tree.
2. Logical query plan: Transforms parse tree into expression tree of relational algebra.
3.Physical query plan: Transforms logical query plan into physical query plan.
. Operation performed
. Order of operation
. Algorithm used
. The way in which stored data is obtained and passed from one
operation to another.

4. Form a query to a logical query plan
Parser
Preprocessor
Logical Query plan generator
Query rewrite
Preferred logical query plan
Form a query to a logical query plan

5. Syntax Analysis and Parse Tree
Parser takes the sql query and convert it to parse
tree. Nodes of parse tree:
1. Atoms: known as Lexical elements such as key words, constants, parentheses, operators, and
other schema elements.
2. Syntactic categories: Subparts that plays a
similar role in a query as <Query> , <Condition>

6. Grammar for Simple Subset of SQL
<Query> ::= <SFW>
<Query> ::= (<Query>)‏
<SFW> ::= SELECT <SelList> FROM <FromList> WHERE <Condition>
<SelList> ::= <Attribute>,<SelList>
<SelList> ::= <Attribute>
<FromList> ::= <Relation>, <FromList>
<FromList> ::= <Relation>
<Condition> ::= <Condition> AND <Condition>
<Condition> ::= <Tuple> IN <Query>
<Condition> ::= <Attribute> = <Attribute>
<Condition> ::= <Attribute> LIKE <Pattern>
<Tuple> ::= <Attribute>
Atoms(constants), <syntactic categories>(variable),
::= (can be expressed/defined as)‏

7. Query and Parse T ree StarsIn(title,year,starName)
MovieStar(name,address,gender,birthdate)‏
Query:
Give titles of movies that have at least one star born in 1960
SELECT title FROM StarsIn WHERE starName IN (
SELECT name FROM MovieStar WHERE
birthdate LIKE '%1960%' );

9. Another query equivalent
SELECT title
FROM StarsIn, MovieStar
WHERE starName = name AND
birthdate LIKE '%1960%' ;

10. Parse Tree <Query> <SFW>
SELECT <SelList> FROM <FromList> WHERE <Condition>
<Attribute> <RelName> , <FromList> AND
title StarsIn <RelName>
MovieStar
<Query>
<Condition> <Condition>
<Attribute> = <Attribute> <Attribute> LIKE <Pattern>
starName name birthdate ‘%1960’

11. The Preprocessor Functions of Preprocessor
. If a relation used in the query is virtual view then each use of this relation in the form-list must replace by parser tree that describe the view.
. It is also responsible for semantic checking
1. Checks relation uses : Every relation mentioned in FROM-
clause must be a relation or a view in current schema.
2. Check and resolve attribute uses: Every attribute mentioned
in SELECT or WHERE clause must be an attribute of same relation in the current scope.
3. Check types: All attributes must be of a type appropriate to
their uses.

12. StarsIn(title,year,starName)
MovieStar(name,address,gender,birthdate)‏
Query:
Give titles of movies that have at least one star born in 1960
SELECT title FROM StarsIn WHERE starName IN (
SELECT name FROM MovieStar WHERE
birthdate LIKE '%1960%' );

13. Preprocessing Queries Involving Views
When an operand in a query is a virtual view, the preprocessor needs to replace the operand by a piece of parse tree that represents how the view is constructed from base table.
Base Table: Movies( title, year, length, genre, studioname, producerC#)‏
View definition : CREATE VIEW ParamountMovies AS
SELECT title, year FROM movies
WHERE studioName = 'Paramount';
Example based on view:
SELECT title FROM ParamountMovies WHERE year = 1979;

14. Thank You