SELECT
selection
table-expression
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A select-expression specifies a
result table. It is used in the following Natural SQL statements:
INSERT |
SELECT | UPDATE
This document covers the following topics:
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ALL
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{scalar-expression
[[AS]
correlation-name]},
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DISTINCT
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*
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The selection specifies the
items to be selected.
Duplicate rows are not automatically eliminated from the result of a
select-expression. To request this,
specify the keyword DISTINCT.
The alternative to DISTINCT is ALL.
ALL is assumed if neither is specified.
Instead of, or as well as, simple column names, a selection can also
include general scalar-expressions
containing scalar operators and scalar functions which provide computed values
(see also the section Scalar
Expressions).
Example:
SELECT NAME, 65 - AGE FROM SQL-PERSONNEL ...
A correlation-name can be
assigned to a scalar-expression as
alias name for a result column.
The correlation-name need not
be unique. If no correlation-name is
specified for a result column, the corresponding
column-name will be used (if the result
column is derived from a column name; if not, the result table will have no
name). The name of a result column may be used, for example, as column name in
the ORDER BY clause of a SELECT statement.
All columns of all tables specified in the FROM clause are
selected.
Example:
SELECT * FROM SQL-PERSONNEL, SQL-AUTOMOBILES ...
| from-clause [where-clause] |
| [group-by-clause] [having-clause] |
The table-expression specifies
from where and according to what criteria rows are to be selected.
FROM table-reference,…
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This clause specifies from which tables the result set is built.
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table-name [[ |
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The tables specified in the FROM clause must contain the
column fields used in the selection list.
You can either specify a single table or produce an intermediate table resulting from a subquery or a "join" operation (see below).
Since various tables (that is, DDMs) can be addressed in one
FROM clause and since a
table-expression can contain several
FROM clauses if subqueries
are specified, the database ID (DBID) of the first DDM specified in the first
FROM clause of the whole expression is used to identify the
underlying database involved.
Optionally a correlation-clause
can be assigned to a table-name. For a
subquery, a
correlation-clause must be
assigned.
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table-reference |
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JOIN table-reference
ON join-condition |
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A joined-table specifies an
intermediate table resulting from a "join" operation.
The "join" can be an INNER, LEFT
OUTER, RIGHT OUTER or FULL OUTER
JOIN. If you do not specify anything, INNER
applies.
Multiple "join" operations can be nested; that is, the
tables which create the intermediate result table can themselves be
intermediate result tables of a "join" operation or a
subquery; and the latter, in turn, can
also have a joined-table or another
subquery in its FROM
clause.
For INNER, LEFT OUTER, and RIGHT
OUTER joins:
search-condition |
For FULL OUTER joins:
full-join-expression =
full-join-expression [AND
]
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column-name |
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VALUE
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(column-name
,
)
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COALESCE
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Within a
join-expression only
column-names and the
scalar-function VALUE (or
its synonym COALESCE) are allowed.
See details on column-name.
[WHERE
search-condition]
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The WHERE clause is used a to specify the selection
criteria (search-condition) for the rows to be
selected.
Example:
DEFINE DATA LOCAL 01 NAME (A20) 01 AGE (I2) END-DEFINE ... SELECT * INTO NAME, AGE FROM SQL-PERSONNEL WHERE AGE = 32 END-SELECT ...
See details on search-condition.
[GROUP
BY column-reference,]
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The GROUP BY clause rearranges the table represented by
the FROM clause into groups in a way that all rows within each
group have the same value for the GROUP BY columns.
Each column-reference in the
selection list must be either a GROUP BY column or specified
within an aggregate-function. Aggregate
functions are applied to the individual groups (not to the entire table). The
result table contains as many rows as groups.
See further details on column-reference
and aggregate-function.
Example:
DEFINE DATA LOCAL 1 #AGE (I2) 1 #NUMBER (I2) END-DEFINE ... SELECT AGE , COUNT(*) INTO #AGE, #NUMBER FROM SQL-PERSONNEL GROUP BY AGE ...
If the GROUP BY clause is preceded by a WHERE
clause, all rows that do not satisfy the WHERE clause are excluded
before any grouping is done.
[HAVING
search-condition]
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If the HAVING clause is specified, the GROUP
BY clause should also be specified.
Just as the WHERE clause is used to exclude rows from a
result table, the HAVING clause is used to exclude groups and
therefore also based on a
search-condition. Scalar expressions in
a HAVING clause must be single-valued per group.
See further details on scalar-expression
and search-condition.
Example:
DEFINE DATA LOCAL 1 #NAME (A20) 1 #AVGAGE (I2) 1 #NUMBER (I2) END-DEFINE ... SELECT NAME, AVG(AGE), COUNT(*) INTO #NAME, #AVGAGE, #NUMBER FROM SQL-PERSONNEL GROUP BY NAME HAVING COUNT(*) > 1 ...
