Database Reference
In-Depth Information
Output Table
Input SQL Query
R.a
S.c
x
y
z
...
1
6
4
...
SELECT R.a, S.c
FROM R, S
WHERE R.x=S.y
AND S.b<10
Simplified DBMS
Execution
Engine
Parser
Optimizer
Project
[R.a, S.c]
π
R.a, S.c
Merge Join
[R.x=S.y]
R.x=S.y
R
σ
s.b<10
S
Index Scan
[R]
Sort
[S.y]
Algebraic Tree
Index Scan
[S.b<10]
Query Execution Plan
FIGURE 2.1
Executing SQL queries in a relational database system.
Simplified Query Optimizer
Enumeration
Engine
(e.g., rules)
(Sub) Plans
Explored
Input: Algebraic
tree representing
the input query
Output: Query
execution plan
Cardinality
Estimation
Cost Estimation
FIGURE 2.2
Simplified architecture of a database query optimizer.
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