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ALL | DISTINCT
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The DISTINCT keyword indicates that duplicate values found in two or more rows will not be shown after the first row. The ALL keyword explicitly reinforces the default to retrieve all rows regardless of uniqueness.
Note that the ORDER BY clause sorts rows before the DISTINCT clause removes non-unique rows. Use these clauses together to ensure that the row found is the row you intend to retrieve.
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DISTINCT ON
-
The ON keyword, following the DISTINCT keyword, allows you to specify one or more
distinct_expressions
by which to judge uniqueness.
-
distinct_expression
-
A column name within a
from_item
, or a valid expression, whose value is used by the DISTINCT ON clause as a basis for removing duplicate values.
-
target_expression
-
A column name within a
from_item
, or a valid expression.
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output_name
-
An alternate name for an output column, following the AS clause. This name will then be used during display of the output and can be used to reference the column within ORDER BY and GROUP BY clauses in the same SELECT statement. However, this name does
not
apply to the WHERE or HAVING clauses; you will need to use the correct column name for them.
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FROM
-
The clause which is passed
from_items
, from which to retrieve rows.
-
from_item
-
The name of a table, a subselect, or a JOINed set of
from_items
that you wish to retrieve data from.
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{ , | CROSS JOIN }
-
The comma (or formal CROSS JOIN clause) separates multiple
from_items
.
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WHERE
-
The clause that is passed
conditions
by which to constraint a result set.
-
condition
-
An expression that yields either true or false, applied conditionally to non-grouped target expressions.
-
GROUP BY
-
The clause that is passed
aggregate_expressions
to aggregate (group) rows together.
-
aggregate_expression
-
A column name within a
from_item
, or a valid expression, to be used as a basis to aggregate (group) rows together.
-
HAVING
-
The clause to which is passed any
aggregate_conditions
by which to constrain a result set.
-
aggregate_condition
-
An expression that yields either true or false, applied conditionally to aggregated (grouped) target expressions.
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UNION
-
The clause that combines two result sets with compatible column structure into a single combined result set.
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INTERSECT
-
The clause that removes any rows from the initial result set
not
found in the following
select
statement's result set (resulting in the overlapping, or intersecting, set).
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EXCEPT
-
The clause that removes any rows from the initial result set that
are
found in the following
select
statement's result set (resulting in the difference set).
-
select
-
A full
select
statement. The limitation on this form of subquery is that you cannot use any of the ORDER BY, FOR UPDATE, or LIMIT clauses unless the statement is enclosed in parentheses.
-
ORDER BY
-
The ORDER BY clause sorts the retrieved result set by each
order_expression
provided.
-
order_expression
[ ASC | DESC | USING
operator
]
-
A column name in the retrieved result set by which the ORDER BY clause sorts the results. The use of the ASC keyword explicitly defines the default of ascending sorting, while the DESC implies descending sorting. The USING clause defines an
operator
(e.g., >) to compare subsequent
order_expression
values with.
-
FOR UPDATE
-
The locking clause that places an implicit ROW SHARE MODE lock (see LOCK") on the
from_item
table selected in the current transaction.
-
OF
update_table
-
A specific table to which to apply ROW SHARE MODE locking when multiple tables are selected in the FROM clause.
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LIMIT
-
The LIMIT clause constrains only a specified portion of the retrieved results.
-
ALL |
count
-
The ALL keyword explicitly specifies the default, which is to not limit the number of rows returned. The use of a numeric
count
value limits the number of rows in the retrieved result set to
count
.
-
{ OFFSET | , }
start
-
The OFFSET keyword (or informal comma, following the LIMIT clause) allows a result set to ignore the first
start
rows.
