WHERE Clause

Specifies a search condition to restrict the rows returned.

Syntax

[ WHERE < search_condition > | < old_outer_join > ]

< old_outer_join > ::=
    column_name { * = | = * } column_name

Arguments

< search_condition >

Restricts the rows returned in the result set through the use of predicates. There is no limit to the number of predicates that can be included in a search condition. For more information about search conditions and predicates, see Search Condition.

< old_outer_join >

Specifies an outer join using the nonstandard product-specific syntax and the WHERE clause. The *= operator is used to specify a left outer join and the =* operator is used to specify a right outer join.

This example specifies a left outer join in which the rows from Tab1, that do not meet the specified condition, are included in the result set:

SELECT Tab1.name, Tab2.id
FROM Tab1, Tab2
WHERE Tab1.id *=Tab2.id

Note  Using this syntax for outer joins is discouraged because of the potential for ambiguous interpretation and because it is nonstandard. Instead, specify joins in the FROM clause.

It is possible to specify outer joins by using join operators in the FROM clause or by using the non-standard *= and =* operators in the WHERE clause. The two methods cannot both be used in the same statement.

GROUP BY Clause

Specifies the groups into which output rows are to be placed and, if aggregate functions are included in the SELECT clause <select list>, calculates a summary value for each group. When GROUP BY is specified, either each column in any non-aggregate expression in the select list should be included in the GROUP BY list, or the GROUP BY expression must match exactly the select list expression.

Note  If the ORDER BY clause is not specified, groups returned using the GROUP BY clause are not in any particular order. It is recommended that you always use the ORDER BY clause to specify a particular ordering of the data.

Syntax

[ GROUP BY [ ALL ] group_by_expression [ ,...n ]
        [ WITH { CUBE | ROLLUP } ]
]

Arguments

ALL

Includes all groups and result sets, even those that do not have any rows that meet the search condition specified in the WHERE clause. When ALL is specified, null values are returned for the summary columns of groups that do not meet the search condition. You cannot specify ALL with the CUBE or ROLLUP operators.

GROUP BY ALL is not supported in queries that access remote tables if there is also a WHERE clause in the query.

group_by_expression

Is an expression on which grouping is performed. group_by_expression is also known as a grouping column. group_by expression can be a column or a nonaggregate expression that references a column. A column alias that is defined in the select list cannot be used to specify a grouping column.

Note  Columns of type text, ntext, and image cannot be used in group_by_expression.

For GROUP BY clauses that do not contain CUBE or ROLLUP, the number of group_by_expression items is limited by the GROUP BY column sizes, the aggregated columns, and the aggregate values involved in the query. This limit originates from the limit of 8,060 bytes on the intermediate work table that is needed to hold intermediate query results. A maximum of 10 grouping expressions is permitted when CUBE or ROLLUP is specified.

CUBE

Specifies that in addition to the usual rows provided by GROUP BY, summary rows are introduced into the result set. A GROUP BY summary row is returned for every possible combination of group and subgroup in the result set. A GROUP BY summary row is displayed as NULL in the result, but is used to indicate all values. Use the GROUPING function to determine whether null values in the result set are GROUP BY summary values.

The number of summary rows in the result set is determined by the number of columns included in the GROUP BY clause. Each operand (column) in the GROUP BY clause is bound under the grouping NULL and grouping is applied to all other operands (columns). Because CUBE returns every possible combination of group and subgroup, the number of rows is the same, regardless of the order in which the grouping columns are specified.

ROLLUP

Specifies that in addition to the usual rows provided by GROUP BY, summary rows are introduced into the result set. Groups are summarized in a hierarchical order, from the lowest level in the group to the highest. The group hierarchy is determined by the order in which the grouping columns are specified. Changing the order of the grouping columns can affect the number of rows produced in the result set.

Important  Distinct aggregates, for example, AVG(DISTINCT column_name), COUNT(DISTINCT column_name), and SUM(DISTINCT column_name), are not supported when using CUBE or ROLLUP. If used, SQL Server returns an error message and cancels the query.