Chapter 12 Joining Tables Part C. SQL Copyright 2005 Radian Publishing Co.
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Chapter 12 Joining Tables
Part C. SQL
Copyright 2005 Radian Publishing Co.
Copyright 2005 Radian Publishing Co.2/27
Contents
Chapter 12 Joining Tables
12.1 Business Applications
12.2 Set Operations
• 12.2 A. Union
• 12.2 B. Intersect
• 12.2 C. Minus
12.3 Other Types of JOIN
• 12.3 A. Cross-join
• 12.3 B. Outer-join
• 12.3 C. Simulating MINUS by Outer-Join
• 12.3 D. Joining to Oneself
• 12.3 E. Bus Routes Using Joining to Oneself
Copyright 2005 Radian Publishing Co.3/27
Chapter 12 Joining Tables
Table joining gathers data from more than one table when retrieving
data from a database.
Join condition may be placed in JOIN clause. It can also be an
inequality.
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12.1 Business Applications
The basic syntax of inner join is:
SELECT …FROM TableName1, TableName2 WHERE JoinCondition [AND FilterCondition]
The filter condition must be written after the join condition.
An alternative syntax for inner-join is:
SELECT ...FROM TableName1INNER JOIN TableName2 ON JoinConditionWHERE FilterCondition
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12.2 Set Operations (1/3)
A join combines tables by columns.
Fig.12.7 Joining tables by columns
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12.2 Set Operations (2/3)
Combining tables by rows requires the original tables to have
compatible structures.
Fig.12.8 Joining tables by rows
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12.2 Set Operations (3/3)
We shall discuss three mathematical set operations:
• UNION• INTERSECT• MINUS
Fig.12.9 The three set operations
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12.2 A. Union (1/2)
UNION simply groups the records of two tables together. Duplicated
rows are removed. If duplicated rows are necessary, use UNION ALL.
Syntax for UNION:
SELECT … FROM TableA
UNION
SELECT … FROM TableB
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12.2 A. Union (2/2)
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12.2 B. Intersect (1/2)
INTERSECT selects records which are common to both tables.
Syntax for INTERSECT:
SELECT … FROM TableAINTERSECTSELECT … FROM TableB
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12.2 B. Intersect (2/2)
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12.2 C. Minus
MINUS selects records which are found in one set but not on the other.
Syntax for MINUS:
SELECT … FROM TableAMINUSSELECT … FROM TableB
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12.3 Other Types of JOIN (1/2)
Fig.12.19 All possibletable combination
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12.3 Other Types of JOIN (2/2)
A cross-join is a join without any join condition.
Joins with a join condition are divided into inner-joins and outer-joins.
An inner-join consists of records matching the join conditions. Inner-
joins are further classified into equi-joins and non-equi-joins.
An equi-join uses the equal operator (=) in the join condition.
A non-equi-join uses relational operators, >, <, >=, <=, <>.
A natural join is an equi-join without duplicating columns.
Copyright 2005 Radian Publishing Co.15/27
12.3 A. Cross-join (1/3)
A cross-join is a join without any join condition. It will map every record
in one table with every record in the other table.
Fig.12.20 Cross-joining Table A and Table B
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12.3 A. Cross-join (2/3)
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12.3 A. Cross-join (3/3)
Qualifiers are used to remove ambiguity, where two tables have the
same column name.
Both join condition and filter condition can exist in the WHERE clause.
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12.3 B. Outer-join (1/6)
An outer-join selects both matched and non-matched records.
It is further classified into left-outer-joins, right-outer-joins and full-outer-
joins.
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12.3 B. Outer-join (2/6)
A left-outer-join selects all the rows from the first table including those
match and those do not match the rows in the second table.
The syntax for a left-outer-join is
SELECT ...
FROM TableName1
LEFT OUTER JOIN TableName2
ON JoinCondition
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12.3 B. Outer-join (3/6)
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12.3 B. Outer-join (4/6)
A right-outer-join selects all the rows from the second table including
those match and those do not match the rows in the first table.
Syntax for right-outer-join:
SELECT ...
FROM TableName1
RIGHT OUTER JOIN TableName2
ON JoinCondition
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12.3 B. Outer-join (5/6)
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12.3 B. Outer-join (6/6)
A full-outer-join reveals unmatched records on both sides as well as the matched records.
Syntax for full-outer-join:
SELECT ...
FROM TableName1
FULL OUTER JOIN TableName2
ON JoinCondition
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12.3 C. Simulating MINUS by Outer-Join
Refer to textbook P.286
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12.3 D. Joining to Oneself (1/2)
Joining a table to itself means writing the same table name twice in
FROM clause of the SQL statement.
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12.3 D. Joining to Oneself (2/2)
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12.3 E. Bus Routes Using Joining to Oneself
Refer to textbook P.289
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