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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:

• Selection

• Table Expression

Selection

	ALL			{scalar-expression [[AS] correlation-name]},
	DISTINCT			*

The selection specifies the items to be selected.

ALL/DISTINCT

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.

Scalar Expression

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 
  ...

Correlation Name

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.

Asterisk Notation - *

All columns of all tables specified in the FROM clause are selected.

Example:

SELECT * 
  FROM SQL-PERSONNEL, SQL-AUTOMOBILES 
  ...

Table Expression

The table-expression specifies from where and according to what criteria rows are to be selected.

FROM Clause

This clause specifies from which tables the result set is built.

Table Reference

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.

The TABLE function-name clause belongs to the SQL Extended Set and requires a correlation-clause with a column-name list.

Optionally a correlation-clause can be assigned to a table-name. For a subquery, a correlation-clause must be assigned.

Correlation Clause

A correlation-clause consists of optional keyword AS and a correlation-name and is optionally followed by a plain column-name list. The column-name list belongs to the SQL Extended Set.

Joined Table

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.

Join Condition

For INNER, LEFT OUTER, and RIGHT OUTER joins:

For FULL OUTER joins:

full-join-expression = full-join-expression [AND ]

Full Join Expression

	column-name
		VALUE		(column-name , )
		COALESCE

Within a join-expression only column-names and the scalar-function VALUE (or its synonym COALESCE) are allowed. See details on column-name.

data-change-table-reference

A data-change-table-reference specifies an intermediate result table, which is base on the rows that are changed by the SQL change statement specified in the clause. A data-change-table-reference can only be specified as the only table reference in the FROM clause.

XMLTABLE Function

The item xmltable-function specifies an invocation of the built-in XMLTABLE function.

WHERE Clause

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 Clause

[GROUP BY column-reference,]

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 Clause

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 
  ...

ORDER BY Clause

ORDER BY		sort-key		ASC		,
				DESC
		INPUT SEQUENCE
		ORDER OF table-designator

sort-key

FETCH FIRST Clause

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