SELECT - SQL

This document covers the following topics:

Belongs to Function Group: Database Access and Update


Function

The SELECT statement supports both the cursor-oriented selection that is used to retrieve an arbitrary number of rows and the non-cursor selection (singleton SELECT) that retrieves at most one single row. With the SELECT ... END-SELECT construction, Natural uses the same database loop processing as with the FIND statement.

Two different structures are possible.

Syntax 1 - Cursor-Oriented Selection

Like the Natural FIND statement, the cursor-oriented SELECT statement is used to select a set of rows (records) from one or more DB2 tables, based on a search criterion. Since a database loop is initiated, the loop must be closed by a LOOP (reporting mode) or END-SELECT statement. With this construction, Natural uses the same loop processing as with the FIND statement.

In addition, no cursor management is required from the application program; it is automatically handled by Natural.

Common Set Syntax:

SELECT   selection INTO

parameter,
VIEW {view-name [correlation-name]},

table-expression      

UNION

[ALL] [(]SELECT   selection table-expression[)]

EXCEPT
INTERSECT
ORDER BY

integer

ASC
DESC

 
column-reference
expression
statement
END-SELECT (structured mode only)            
LOOP       (reporting mode only)

Extended Set Syntax:

[WITH_CTE common-table-expression,...]
SELECT selection  INTO  

parameter,
VIEW {view-name [correlation-name]},

table-expression      

UNION
EXCEPT
INTERSECT

[ALL] [(]SELECT selection table-expression[)]

           
  ORDER BY Clause
  [OPTIMIZE FOR integer ROWS]

WITH

CS

                                     
RR
UR
RS
RS KEEP UPDATE LOCKS
RR KEEP UPDATE LOCKS
  QUERYNO integer

FETCH FIRST

1

ROW

ONLY

                         
integer ROWS
  [WITH HOLD]
  [WITH RETURN]

WITH

ASENSITIVE SCROLL

[:]scroll_hv [GIVING [:] sqlcode

                     
INSENSITIVE SCROLL
SENSITIVE STATIC SCROLL
SENSITIVE DYNAMIC SCROLL

WITH ROWSET POSITIONING FOR

[:] row_hv

ROWS

ROWS_RETURNED [:] ret_row

                     
integer
  [IF-NO-RECORDS-FOUND-clause]
   statement
END-SELECT (structured mode only)                                              
LOOP (reporting mode only)

For an explanation of the symbols used in the syntax diagram, see Syntax Symbols.

Syntax Element Description - Syntax 1:

Syntax Element Description
INTO
INTO Clause:

The INTO clause is used to specify the target fields in the program which are to be filled with the result of the selection. For further information and examples, see INTO Clause below.

VIEW
VIEW Clause:

If one or more views are referenced in the INTO clause, the number of items specified in the selection must correspond to the number of fields defined in the view(s) (not counting group fields, redefining fields and indicator fields). For further information and examples, see VIEW Clause below.

table-expression
Table Expression:

A table-expression consists of a FROM clause and an optional WHERE clause.

For further information, see table-expression.

UNION
Query Involving UNION Clause:

UNION unites the results of two or more select expressions. For further information and an example, see Query Involving UNION below.

ALL
Including Redundant Rows:

Specifies the result set contains redundant (duplicate) rows.

ORDER BY
ORDER BY Clause:

The ORDER BY clause arranges the result of a SELECT statement in a particular sequence. For further information and examples; see ORDER BY Clause below.

IF NO RECORDS FOUND
IF NO RECORDS FOUND Clause:

The IF NO RECORDS FOUND clause is used to initiate a processing loop if no records meet the selection criteria specified in the preceding SELECT statement. For further information, see IF NO RECORDS FOUND Clause below.

END-SELECT
End of SELECT Statement:

In structured mode, the Natural reserved keyword END-SELECT must be used to end the SELECT statement.

In reporting mode, the LOOP statement must be used to end the SELECT statement.

LOOP
The following syntax elements belong to the SQL Extended Set:
WITH_CTE common-table-expression,...
WITH_CTE Clause:

This optional clause allows you to define a result table which can be referenced in any FROM clause of the SELECT that follows. Multiple common-table-expressions can be specified following the single WITH_CTE keyword. Each common-table-expression can also be referenced in the FROM clause of a subsequent common-table-expression.

For further information, see WITH CTE common-table-expression,... below.

OPTIMIZE FOR
OPTIMIZE FOR Clause:

This clause is only valid against DB2 databases. When used against other databases, it will cause runtime errors.

WITH CS/RS/UR/...
WITH CS/RS/UR/... Clause:

This clause is only valid against DB2 databases. When used against other databases, it will cause runtime errors.

QUERYNO
QUERYNO Clause:

The QUERYNO clause specifies the number to be used for this SQL statement in EXPLAIN output and trace records.

SKIP LOCKED DATA
SKIP LOCKED DATA Clause:

The SKIP LOCKED DATA clause specifies that rows are skipped when incompatible locks are held on the row by other transactions.

FETCH FIRST
FETCH FIRST Clause:

This clause is only valid against DB2 databases. When used against other databases, it will cause runtime errors.

WITH HOLD
WITH HOLD Clause:

This clause is not currently supported. When used, it will cause a compiler error.

WITH RETURN
WITH RETURN Clause:

This clause is not currently supported. When used, it will cause a compiler error.

WITH ... SCROLL
WITH ... SCROLL Clause:

RDBMS scrollable cursors are enabled with this clause. Scrollable cursors can be ASENSITIVE, INSENSITIVE, SENSITIVE STATIC or SENSITIVE DYNAMIC.

Note:
Not all SQL database systems support all options.

  • WITH ASENSITIVE SCROLL specifies that the cursor is either INSENSITIVE or SENSITIVE DYNAMIC. This is determined by the database at open time of the cursor, depending on the read-only property of the cursor: If the cursor is read-only, the cursor will become INSENSITIVE. If the cursor is not read-only, the cursor will become SENSITIVE DYNAMIC. This is supported for DB2 databases.

  • WITH INSENSITIVE SCROLL specifies that the cursor is insensitive for updates, deletes and inserts executed against the base table, after the cursor has been updated. Positioned updates and deletes are not allowed against INSENSITIVE SCROLL cursors. This is supported for Oracle, Adabas D, Informix, MS SQL Server ODBC and DB2 databases.

  • WITH SENSITIVE STATIC specifies that the cursor is sensitive for updates and deletes against the base table, but not against inserts, after the cursor has been opened. Positioned updates and deletes are allowed against SENSITIVE STATIC SCROLL cursors. This is supported for Adabas D, MS SQL Server ODBC and DB2 databases.

  • WITH SENSITIVE DYNAMIC specifies that the cursor is sensitive for updates, deletes and inserts against the base table, after the cursor has been opened. Positioned updates and deletes are allowed against SENSITIVE DYNAMIC SCROLL cursors. This is supported for Adabas D, MS SQL Server ODBC and DB2 databases.

Scrollable cursors allow the application to position any row in the cursor at any time as long as the cursor is open. Scrollable cursors are not supported for Sybase databases at all. Scrollable cursors are not supported for the MS SQL Server DBLIB interface, but only for the MS SQL Server ODBC interface.

The positioning is performed depending on the content of the scroll_hv. The content is evaluated each time a FETCH against the database is executed.

WITH ROWSET POSITIONING FOR … ROWS
WITH ROWSET POSITIONING FOR … ROWS Clause:

This clause enables DB2 rowset processing, which corresponds to Natural native DML multi-fetch processing. [:] row_hv (I4) or integer determines the maximum number of rows returned from DB2 to Natural. The number determines either the size of the Natural multi-fetch buffer used for standard multiple row processing or the maximum number of rows returned from DB2 into the Natural program for advanced multiple row processing.

ROWS_RETURNED [:] ret_row
ROWS_RETURNED [:] ret_row Clause:

This clause specifies an I4 variable which will receive the number of rows returned by DB2 on behalf of the last executed DB2 fetch operation for advanced multiple row processing.

INTO Clause

INTO

parameter,
VIEW {view-name [correlation-name ]},

The INTO clause is used to specify the target fields in the program which are to be filled with the result of the selection.

The INTO clause can specify either single parameters or one or more views as defined in the DEFINE DATA statement.

All target field values can come either from a single table or from more than one table as a result of a join operation (see also Join Queries).

Note:
In standard SQL syntax, an INTO clause is only used in non-cursor select operations (singleton SELECT) and can be specified only if a single row is to be selected. In Natural, however, the INTO clause is used for both cursor-oriented and non-cursor select operations.

The selection can also merely consist of an asterisk (*). In a standard select expression, this is a shorthand for a list of all column names in the table(s) specified in the FROM clause. In the Natural SELECT statement, however, the same syntactical item SELECT * has a different semantic meaning: all the items listed in the INTO clause are also used in the selection. Their names must correspond to names of existing database columns.

Examples:

Example 1:

DEFINE DATA LOCAL
01 PERS VIEW OF SQL-PERSONNEL  
  02 NAME
  02 AGE
END-DEFINE
...
SELECT *
  INTO NAME, AGE

Example 2:

...
SELECT *
  INTO VIEW PERS

These examples are equivalent to the following ones:

Example 3:

...
SELECT NAME, AGE  
  INTO NAME, AGE

Example 4:

...
SELECT NAME, AGE  
  INTO VIEW PERS

VIEW Clause

VIEW {view-name [correlation-name]},

If one or more views are referenced in the INTO Clause, the number of items specified in the selection must correspond to the number of fields defined in the view(s) (not counting group fields, redefining fields and indicator fields).

Note:
Both the Natural target fields and the table columns must be defined in a Natural DDM. Their names, however, can be different, since assignment is made according to their sequence.

Example of INTO clause with view:

DEFINE DATA LOCAL
01 PERS VIEW OF SQL-PERSONNEL   
  02 NAME
  02 AGE
END-DEFINE
...
SELECT FIRSTNAME, AGE
  INTO VIEW PERS
  FROM SQL-PERSONNEL
...

The target fields NAME and AGE, which are part of a Natural view, receive the contents of the table columns FIRSTNAME and AGE.

Syntax Element Description:

Syntax Element Description
parameter

If single parameters are specified as target fields, their number and formats must correspond to the number and formats of the columns and/or scalar-expressions specified in the corresponding selection as described above (for details, see Scalar Expressions).

Example:

DEFINE DATA LOCAL
01 #NAME   (A20)
01 #AGE    (I2)
END-DEFINE
...
SELECT NAME, AGE
  INTO #NAME, #AGE
  FROM SQL-PERSONNEL   
...

The target fields #NAME and #AGE, which are Natural program variables, receive the contents of the table columns NAME and AGE.

correlation-name

If the VIEW clause is used within a SELECT * construction where multiple tables are to be joined, correlation-names are required if the specified view contains fields that reference columns which exist in more than one of these tables. In order to know which column to select, all these columns are qualified by the specified correlation-name at generation of the selection list. The correlation-name assigned to a view must correspond to one of the correlation-names used to qualify the tables to be joined. See also the section Join Queries.

Example:

DEFINE DATA LOCAL
01 PERS VIEW OF SQL-PERSONNEL
  02 NAME
  02 FIRST-NAME
  02 AGE
END-DEFINE
...
SELECT *
  INTO VIEW PERS A
  FROM SQL-PERSONNEL A, SQL-PERSONNEL B  
...

Query Involving UNION

Note:
In the following, the term "SELECT statement" is used as a synonym for the whole query-expression consisting of multiple select expressions concatenated with UNION.

UNION unites the results of two or more select-expressions. The columns specified in the individual select-expressions must be UNION-compatible; that is, matching in number, type and format.

Redundant duplicate rows are always eliminated from the result of a UNION unless the UNION operator explicitly includes the ALL qualifier. With UNION, however, there is no explicit DISTINCT option as an alternative to ALL.

Example:

DEFINE DATA LOCAL
01 PERS VIEW OF SQL-PERSONNEL   
  02 NAME
  02 AGE
  02 ADDRESS (1:6)
END-DEFINE
...
SELECT NAME, AGE, ADDRESS
  INTO VIEW PERS
  FROM SQL-PERSONNEL
  WHERE AGE > 55
UNION ALL
SELECT NAME, AGE, ADDRESS
  FROM SQL-EMPLOYEES
  WHERE PERSNR < 100
ORDER BY NAME
...
END-SELECT
...

In general, any number of select-expressions can be concatenated with UNION.

The INTO clause must be specified with the first select-expression only.

ORDER BY Clause

ORDER BY

integer

ASC

 
column-reference DESC

The ORDER BY clause arranges the result of a SELECT statement in a particular sequence.

Each ORDER BY clause must specify a column of the result table. In most ORDER BY clauses a column can be identified either by column-reference (that is, by an optionally qualified column name) or by column number. In a query involving UNION, a column must be identified by column number. The column number is the ordinal left-to-right position of a column within the selection, which means it is an integer value. This feature makes it possible to order a result on the basis of a computed column which does not have a name.

Example:

DEFINE DATA LOCAL
1 #NAME          (A20)
1 #YEARS-TO-WORK (I2)
END-DEFINE
...
SELECT NAME , 65 - AGE
  INTO #NAME, #YEARS-TO-WORK   
  FROM SQL-PERSONNEL
  ORDER BY 2
  ...

Ascending or Descending Order

The order specified in the ORDER BY clause can be either ascending (ASC) or descending (DESC). ASC is the default.

Example:

DEFINE DATA LOCAL
1 PERS VIEW OF SQL-PERSONNEL
1 NAME
1 AGE
1 ADDRESS   (1:6)
END-DEFINE
...
SELECT NAME, AGE, ADDRESS
  INTO VIEW PERS
  FROM SQL-PERSONNEL
  WHERE AGE = 55
  ORDER BY NAME DESC
  ...

See further information on integer values and column-reference.

WITH_CTE common-table-expression,…

This clause permits to define result tables that can be referenced in any FROM clause of the SELECT statement that follows.

The Natural specific keyword WITH_CTE corresponds to the SQL keyword WITH. WITH_CTE will be translated into the SQL keyword WITH by the Natural compiler.

Each common-table-expression has to obey the following syntax:

[common-table-expression-name [(column-name,…)] AS (fullselect) ]

Syntax Element Description:

Syntax Element Description
common-table-expression-name Has to be an unqualified SQL identifier and must be different from any other common-table-expression-name specified in the same statement.

Each common-table-expression-name can be specified in the FROM clause of any common-table-expression-name following or in the FROM clause of the SELECT statement following.

column-name Has to be an unqualified SQL identifier and must be unique within one common-table-expression-name.
AS (fullselect) The number of column-names must match the number of columns of the fullselect.

A common-table-expression can be used

  • in place of a view to avoid creating the view;

  • when the same result table needs to be shared in a fullselect;

  • when the result needs to be derived using recursion.

Queries using recursion are useful in applications such as bill of material.

Example:

WITH_CTE                                                        
 RPL (PART,SUBPART,QUANTITY) AS                                 
 (SELECT ROOT.PART,ROOT.SUBPART,ROOT.QUANTITY                   
    FROM HGK-PARTLIST ROOT                                      
   WHERE ROOT.PART ='01'                                       
  UNION ALL                                                     
  SELECT CHILD.PART,CHILD.SUBPART,CHILD.QUANTITY                
    FROM  RPL PARENT, HGK-PARTLIST CHILD                        
    WHERE PARENT.SUBPART = CHILD.PART                            
  )                                                             
SELECT DISTINCT PART,SUBPART,QUANTITY                           
  INTO VIEW V1                                                  
  FROM RPL                                                      
  ORDER BY PART,SUBPART,QUANTITY                                
END-SELECT

OPTIMIZE FOR integer ROWS Clause

[OPTIMIZE FOR integer ROWS]

The OPTIMIZE FOR integer ROWS clause is used to inform DB2 in advance of the number (integer) of rows to be retrieved from the result table. Without this clause, DB2 assumes that all rows of the result table are to be retrieved and optimizes accordingly.

This optional clause is useful if you know how many rows are likely to be selected, because optimizing for integer rows can improve performance if the number of rows actually selected does not exceed the integer value (which can be in the range from 0 to 2147483647).

Example:

SELECT name INTO 
#name FROM table WHERE AGE = 2 OPTIMIZE FOR 100 ROWS

WITH - Isolation Level Clause

WITH

CS
RR
RR KEEP UPDATE LOCK
RS
RS KEEP UPDATE LOCKS
UR

This WITH clause allows you to specify an explicit isolation level with which the statement is to be executed. The following options are provided:

Option Meaning
CS Cursor Stability
RR Repeatable Read
RR KEEP UPDATE LOCKS Only valid if a FOR UPDATE OF clause is specified.

Repeatable Read and retaining update locks.

RS Read Stability
RS KEEP UPDATE LOCKS Only valid if a FOR UPDATE OF clause is specified.

Read Stability and retaining update locks.

UR Uncommitted Read

WITH UR can only be specified within a SELECT statement and when the table is read-only. The default isolation level is determined by the isolation of the package or plan into which the statement is bound. The default isolation level also depends on whether the result table is read-only or not. To find out the default isolation level, refer to the IBM literature.

Note:
This option also works for non-cursor selection.

FETCH FIRST Clause

FETCH FIRST

1
integer

ROW
ROWS

ONLY

The FETCH FIRST clause limits the number of rows to be fetched. It improves the performance of queries with potentially large result sets if only a limited number of rows is needed.

WITH ... SCROLL Clause

WITH

ASENSITIVE SCROLL
INSENSITIVE SCROLL
SENSITIVE STATIC SCROLL
SENSITIVE DYNAMIC SCROLL

[:] scroll_hv [GIVING [:] sqlcode]

Natural supports SQL scrollable cursors by using the clauses WITH ASENSITIVE SCROLL, WITH SENSITIVE STATIC SCROLL and SENSITVE DYNAMIC SCROLL. Scrollable cursors allow Natural applications to position randomly any row in a result set. With non-scrollable cursors, the data can only be read sequentially, from top to bottom.

Syntax Element Description
ASENSITIVE SCROLL ASENSITIVE scrollable cursors are either INSENSITIVE - if the cursor is READ-ONLY - or SENSITIVE DYNAMIC - if the cursor is not READ-ONLY.
INSENSITIVE SCROLL INSENSITIVE SCROLL refers to a cursor that cannot be used in Positioned UPDATE or Positioned DELETE operations. In addition, once opened, an INSENSITIVE SCROLL cursor does not reflect UPDATE, DELETE or INSERT operations against the base table after the cursor was opened.

See also Note.

SENSITIVE STATIC SCROLL SENSITIVE STATIC SCROLL refers to a cursor that can be used for Positioned UPDATEs or Positioned DELETE operations. In addition, a SENSITIVE STATIC SCROLL cursor reflects UPDATE and DELETE operations of base table rows. The cursor does not reflect INSERT operations.

See also Note.

SENSITIVE DYNAMIC SCROLL SENSITIVE DYNAMIC scrollable cursors reflect UPDATE, DELETE and INSERT operations against the base table while the cursor is open.

Note:
INSENSITIVE and SENSITIVE STATIC scrollable cursors use temporary result tables and require a TEMP database in DB2 (see the relevant DB2 literature by IBM).

Below is information on:

scroll_hv

The variable scroll_hv must be alphanumeric.

The variable scroll_hv specifies which row of the result table will be fetched during one execution of the database processing loop. The contents of scroll_hv is evaluated each time the database processing loop cycle is executed.

INSENSITIVE
SENSITVE

CURRENT
FIRST
LAST
PRIOR
NEXT

ABSOLUTE
RELATIVE

+
-

integer

scroll_hv Options

Option Explanation
CURRENT Fetches the current row (again).
FIRST Fetches the first row.
LAST Fetches the last row.
NEXT Fetches the row after the current one. This is the default value.
PRIOR Fetch the row before the current one.
+/- integer

Only applies in connection with ABSOLUTE or RELATIVE.

Specifies the position of the row to be fetched ABSOLUTE or RELATIVE.

Enter a plus (+) or minus (-) sign followed by an integer.

The default value is a plus (+).

ABSOLUTE

Only applies in connection with +/- integer.

Uses integer as the absolute position within the result set from where the row is fetched.

RELATIVE

Only applies in connection with +/- integer.

Uses integer as the relative position to the current position within the result set from where the row is fetched.

There are some restrictions for special RDBMS systems:

  • DB2 does not support the keyword CURRENT.

  • In a SELECT FOR UPDATE loop DB2 only supports NEXT as scrolling option.

  • MS SQL Server (ODBC interface) does not support the keyword CURRENT.

  • Adabas D does not support RELATIVE scrolling.

GIVING [:] sqlcode

The specification of GIVING [:] sqlcode is optional. If specified, the Natural variable [:] sqlcode must be of format I4. The values for this variable are returned from the DB2 SQLCODE of the underlying FETCH operation. This allows the application to react to different statuses encountered while the scrollable cursor is open. The most important status codes indicated by SQLCODE are listed in the following table:

SQLCODE Explanation
0 FETCH operation successful, data returned except for FETCH with option BEFORE or AFTER.
+100 Row not found, cursor still open, no data returned.
-1 General error while trying to FETCH a row

If you specify GIVING [:] sqlcode, the application must react to the different statuses. If an SQLCODE +100 is entered five times successively and without terminal I/O, the Natural for DB2 runtime will issue Natural error NAT3296 in order to avoid application looping. The application can terminate the processing loop by executing an ESCAPE statement.

If you do not specify GIVING [:] sqlcode, except for SQLCODE 0 and SQLCODE +100, each SQLCODE will generate Natural error NAT3700 and the processing loop will be terminated. SQLCODE +100 (row not found) will terminate the processing loop.

See also the example program DEM2SCRL supplied in the Natural system library SYSDB2.

IF NO RECORDS FOUND-Clause

Note:
This clause actually does not belong to Natural SQL; it represents Natural functionality which has been made available to SQL loop processing.

Structured Mode Syntax

IF NO [RECORDS] [FOUND]  

ENTER

statement
END-NOREC

Reporting Mode Syntax

IF NO [RECORDS] [FOUND]

ENTER

statement
DO statement DOEND

 The IF NO RECORDS FOUND clause is used to initiate a processing loop if no records meet the selection criteria specified in the preceding SELECT statement.

If no records meet the specified selection criteria, the IF NO RECORDS FOUND clause causes the processing loop to be executed once with an "empty" record. If this is not desired, specify the statement ESCAPE BOTTOM within the IF NO RECORDS FOUND clause.

If one or more statements are specified with the IF NO RECORDS FOUND clause, the statements are executed immediately before the processing loop is entered. If no statements are to be executed before entering the loop, the keyword ENTER must be used.

Note:
If the result set of the SELECT statement consists of a single row of NULL values, the IF NO RECORDS FOUND clause is not executed. This could occur if the selection list consists solely of one of the aggregate functions SUM, AVG, MIN or MAX on columns, and the set on which these aggregate functions operate is empty. When you use these aggregate functions in the above-mentioned way, you should therefore check the values of the corresponding null-indicator fields instead of using an IF NO RECORDS FOUND clause.

Database Values

Unless other value assignments are made in the statements accompanying an IF NO RECORDS FOUND clause, Natural resets to empty all database fields which reference the file specified in the current loop.

Evaluation of System Functions

Natural system functions are evaluated once for the empty record that is created for processing as a result of the IF NO RECORDS FOUND clause.

Syntax 2 - Non-Cursor Selection

Common Set Syntax:

SELECT SINGLE
  selection  INTO

parameter ,

table-expression      
VIEW {view-name [correlation-name ]},
  [IF-NO-RECORDS-FOUND-clause]
  statement

END-SELECT (structured mode only)

                                     
LOOP (reporting mode only)

Extended Set Syntax:

SELECT SINGLE
  selection  INTO

parameter ,

table-expression      
VIEW {view-name [correlation-name ]},

WITH

CS

                               
RR
UR

FETCH FIRST

1

ROW

ONLY

                   
integer ROWS
  [IF-NO-RECORDS-FOUND-clause]
  statement

END-SELECT (structured mode only)

                                     
LOOP (reporting mode only)

For an explanation of the symbols used in the syntax diagram, see Syntax Symbols.

Syntax Element Description - Syntax 2:

The SELECT SINGLE statement supports the functionality of a non-cursor selection (singleton SELECT); that is, a select expression that retrieves at most one row without using a cursor. It cannot be referenced by a positioned UPDATE or a positioned DELETE statement.

Syntax Element Description
INTO
INTO Clause:

The INTO clause is used to specify the target fields in the program which are to be filled with the result of the selection.

For further information and examples, see INTO Clause.

VIEW
VIEW Clause:

If one or more views are referenced in the INTO clause, the number of items specified in the selection must correspond to the number of fields defined in the view(s) (not counting group fields, redefining fields and indicator fields).

For further information and examples, see VIEW Clause.

table-expression
Table Expression:

The table-expression consists of a FROM clause and optionally of a WHERE clause, a GROUP BY clause and a HAVING clause.

For further information, see selection and table-expression.

WITH CS/RR/UR
WITH - Isolation Level Clause:

This clause is only valid against DB2 databases. When used against other databases, it will cause runtime errors.

CS Cursor Stability
RR Repeatable Read
UR Uncommitted Read
FETCH FIRST
FETCH FIRST Clause:

The FETCH FIRST clause limits the number of rows to be fetched. It improves the performance of queries with potentially large result sets if only a limited number of rows is needed.

IF NO RECORDS FOUND
IF NO RECORDS FOUND Clause:

This clause is used to initiate a processing loop if no records meet the selection criteria specified in the preceding SELECT statement.

For further information, see IF NO RECORDS FOUND Clause.

END-SELECT
LOOP

End of SELECT Statement:

In structured mode, the Natural reserved keyword END-SELECT must be used to end the SELECT statement.

In reporting mode, the LOOP statement must be used to end the SELECT statement.

Join Queries

A join is a query in which data is retrieved from more than one table. All the tables involved must be specified in the FROM clause.

Example:

DEFINE DATA LOCAL
1 #NAME     (A20)
1 #MONEY    (I4)
END-DEFINE
...
SELECT NAME, ACCOUNT
  INTO #NAME, #MONEY
  FROM  SQL-PERSONNEL P, SQL-FINANCE F   
  WHERE P.PERSNR = F.PERSNR
    AND F.ACCOUNT > 10000
    ...

A join always forms the Cartesian product of the tables listed in the FROM clause and later eliminates from this Cartesian product table all the rows that do not satisfy the join condition specified in the WHERE clause.

Correlation names can be used to save writing if table names are rather long. Correlation names must be used when a column specified in the selection list exists in more than one of the tables to be joined in order to know which of the identically named columns to select.