| Programmer's Guide to the Oracle Precompilers Release 1.8 Part Number A42525-1 |
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| Programmer's Guide to the Oracle Precompilers Release 1.8 Part Number A42525-1 |
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View PDF |
This chapter helps you to understand and apply the basic techniques of embedded SQL programming. You learn how to use host variables, indicator variables, cursors, cursor variables, and the fundamental SQL commands that insert, update, select, and delete Oracle data.
Oracle uses host variables to pass data and status information to your program; your program uses host variables to pass data to Oracle.
Depending on how they are used, host variables are called output or input host variables. Host variables in the INTO clause of a SELECT or FETCH statement are called output host variables because they hold column values output by Oracle. Oracle assigns the column values to corresponding output host variables in the INTO clause.
All other host variables in a SQL statement are called input host variables because your program inputs their values to Oracle. For example, you use input host variables in the VALUES clause of an INSERT statement and in the SET clause of an UPDATE statement. They are also used in the WHERE, HAVING, and FOR clauses. In fact, input host variables can appear in a SQL statement wherever a value or expression is allowed.
Attention: In an ORDER BY clause, you can use a host variable, but it is treated as a constant or literal, and hence the contents of the host variable have no effect. For example, the SQL statement
EXEC SQL SELECT ename, empno INTO :name, :number
FROM emp
ORDER BY :ord;
appears to contain an input host variable, ord. However, the host variable in this case is treated as a constant, and regardless of the value of ord, no ordering is done.
You cannot use input host variables to supply SQL keywords or the names of database objects. Thus, you cannot use input host variables in data definition statements (sometimes called DDL) such as ALTER, CREATE, and DROP. In the following example, the DROP TABLE statement is invalid:
EXEC SQL BEGIN DECLARE SECTION;
table_name CHARACTER(30);
EXEC SQL END DECLARE SECTION;
display 'Table name? ';
read table_name;
EXEC SQL DROP TABLE :table_name; -- host variable not allowed
Before Oracle executes a SQL statement containing input host variables, your program must assign values to them. Consider the following example:
EXEC SQL BEGIN DECLARE SECTION;
emp_number INTEGER;
emp_name CHARACTER(20);
EXEC SQL END DECLARE SECTION;
-- get values for input host variables
display 'Employee number? ';
read emp_number;
display 'Employee name? ';
read emp_name;
EXEC SQL INSERT INTO EMP (EMPNO, ENAME)
VALUES (:emp_number, :emp_name);
Notice that the input host variables in the VALUES clause of the INSERT statement are prefixed with colons.
You can associate any host variable with an optional indicator variable. Each time the host variable is used in a SQL statement, a result code is stored in its associated indicator variable. Thus, indicator variables let you monitor host variables.
You use indicator variables in the VALUES or SET clause to assign nulls to input host variables and in the INTO clause to detect nulls or truncated values in output host variables.
For input host variables, the values your program can assign to an indicator variable have the following meanings:
-1
Oracle will assign a null to the column, ignoring the value of the host variable.
>= 0
Oracle will assigns the value of the host variable to the column.
For output host variables, the values Oracle can assign to an indicator variable have the following meanings:
-2
Oracle assigned a truncated column value to the host variable, but could not assign the original length of the column value to the indicator variable because the number was too large.
-1
The column value is null, so the value of the host variable is indeterminate.
0
Oracle assigned an intact column value to the host variable.
> 0
Oracle assigned a truncated column value to the host variable, assigned the original column length (expressed in characters, instead of bytes, for multi-byte NLS host variables) to the indicator variable, and set SQLCODE in the SQLCA to zero.
Remember, an indicator variable must be defined in the Declare Section as a 2-byte integer and, in SQL statements, must be prefixed with a colon and appended to its host variable (unless you use the keyword INDICATOR).
You can use indicator variables to insert nulls. Before the insert, for each column you want to be null, set the appropriate indicator variable to -1, as shown in the following example:
set ind_comm = -1;
EXEC SQL INSERT INTO EMP (EMPNO, COMM)
VALUES (:emp_number, :commission:ind_comm);
The indicator variable ind_comm specifies that a null is to be stored in the COMM column.
You can hardcode the null instead, as follows:
EXEC SQL INSERT INTO EMP (EMPNO, COMM)
VALUES (:emp_number, NULL);
While this is less flexible, it might be more readable.
Typically, you insert nulls conditionally, as the next example shows:
display 'Enter employee number or 0 if not available: ';
read emp_number;
IF emp_number = 0 THEN
set ind_empnum = -1; ELSE
set ind_empnum = 0;
ENDIF;
EXEC SQL INSERT INTO EMP (EMPNO, SAL)
VALUES (:emp_number:ind_empnum, :salary);
You can also use indicator variables to manipulate returned nulls, as the following example shows:
EXEC SQL SELECT ENAME, SAL, COMM
INTO :emp_name, :salary, :commission:ind_comm
FROM EMP
WHERE EMPNO = :emp_number;
IF ind_comm = -1 THEN
set pay = salary; -- commission is null; ignore it
ELSE
set pay = salary + commission;
ENDIF;
When DBMS=V6, you can select or fetch nulls into a host variable that lacks an indicator variable, as the following example shows:
-- assume that commission is NULL
EXEC SQL SELECT ENAME, SAL, COMM
INTO :emp_name, :salary, :commission
FROM EMP
WHERE EMPNO = :emp_number;
SQLCODE in the SQLCA is set to zero indicating that Oracle executed the statement without detecting an error or exception.
However, when DBMS=V7 (the default), if you select or fetch nulls into a host variable that lacks an indicator variable, Oracle issues the following error message:
ORA-01405: fetched column value is NULL
For more information about the option DBMS, see page 6 - 16.
You can use indicator variables in the WHERE clause to test for nulls, as the following example shows:
EXEC SQL SELECT ENAME, SAL
INTO :emp_name, :salary
FROM EMP
WHERE :commission:ind_comm IS NULL ...
However, you cannot use a relational operator to compare nulls with each other or with other values. For example, the following SELECT statement fails if the COMM column contains one or more nulls:
EXEC SQL SELECT ENAME, SAL
INTO :emp_name, :salary
FROM EMP
WHERE COMM = :commission:ind_comm;
The next example shows how to compare values for equality when some of them might be nulls:
EXEC SQL SELECT ENAME, SAL
INTO :emp_name, :salary
FROM EMP
WHERE (COMM = :commission) OR ((COMM IS NULL) AND
(:commission:ind_comm IS NULL));
When DBMS=V6, if you select or fetch a truncated column value into a host variable that lacks an indicator variable, Oracle issues the following error message:
ORA-01406: fetched column value was truncated
However, when DBMS=V7, no error is generated.
Executable SQL statements let you query, manipulate, and control Oracle data and create, define, and maintain Oracle objects such as tables, views, and indexes. This chapter focuses on data manipulation statements (sometimes called DML) and cursor control statements. The following SQL statements let you query and manipulate Oracle data:
SELECT
Returns rows from one or more tables.
INSERT
Adds new rows to a table.
UPDATE
Modifies rows in a table.
DELETE
Removes rows from a table.
When executing a data manipulation statement such as INSERT, UPDATE, or DELETE, your only concern, besides setting the values of any input host variables, is whether the statement succeeds or fails. To find out, you simply check the SQLCA. (Executing any SQL statement sets the SQLCA variables.) You can check in the following two ways:
Alternatively, when MODE={ANSI|ANSI14}, you can check the status variable SQLSTATE or SQLCODE. For more information, see "Using Status Variables when MODE={ANSI|ANSI14} ![[*]](jump.gif)
.
When executing a SELECT statement (query), however, you must also deal with the rows of data it returns. Queries can be classified as follows:
Queries that return more than one row require an explicitly declared cursor or cursor variable (or the use of host arrays, which are discussed, "Using Host Arrays"). The following embedded SQL statements let you define and control an explicit cursor:
DECLARE
Names the cursor and associates it with a query.
OPEN
Executes the query and identifies the active set.
FETCH
Advances the cursor and retrieves each row in the active set, one by one.
CLOSE
Disables the cursor (the active set becomes undefined).
In the coming sections, first you learn how to code INSERT, UPDATE, DELETE, and single-row SELECT statements. Then, you progress to multi-row SELECT statements. For a detailed discussion of each statement and its clauses, see the Oracle7 Server SQL Reference.
Querying the database is a common SQL operation. To issue a query you use the SELECT statement. In the following example, you query the EMP table:
EXEC SQL SELECT ENAME, JOB, SAL + 2000
INTO :emp_name, :job_title, :salary
FROM EMP
WHERE EMPNO = :emp_number;
The column names and expressions following the keyword SELECT make up the select list. The select list in our example contains three items. Under the conditions specified in the WHERE clause (and following clauses, if present), Oracle returns column values to the host variables in the INTO clause. The number of items in the select list should equal the number of host variables in the INTO clause, so there is a place to store every returned value.
In the simplest case, when a query returns one row, its form is that shown in the last example (in which EMPNO is a unique key). However, if a query can return more than one row, you must fetch the rows using a cursor or select them into a host array.
If a query is written to return only one row but might actually return several rows, the result depends on how you specify the option SELECT_ERROR. When SELECT_ERROR=YES (the default), Oracle issues the following error message if more than one row is returned:
ORA-01422: exact fetch returns more than requested number of rows
When SELECT_ERROR=NO, a row is returned and Oracle generates no error.
You can use all of the following standard SQL clauses in your SELECT statements: INTO, FROM, WHERE, CONNECT BY, START WITH, GROUP BY, HAVING, ORDER BY, and FOR UPDATE OF.
You use the INSERT statement to add rows to a table or view. In the following example, you add a row to the EMP table:
EXEC SQL INSERT INTO EMP (EMPNO, ENAME, SAL, DEPTNO)
VALUES (:emp_number, :emp_name, :salary, :dept_number);
Each column you specify in the column list must belong to the table named in the INTO clause. The VALUES clause specifies the row of values to be inserted. The values can be those of constants, host variables, SQL expressions, or pseudocolumns, such as USER and SYSDATE.
The number of values in the VALUES clause must equal the number of names in the column list. However, you can omit the column list if the VALUES clause contains a value for each column in the table in the same order they were defined by CREATE TABLE.
A subquery is a nested SELECT statement. Subqueries let you conduct multipart searches. They can be used to
For example, to copy rows from one table to another, replace the VALUES clause in an INSERT statement with a subquery, as follows:
EXEC SQL INSERT INTO EMP2 (EMPNO, ENAME, SAL, DEPTNO)
SELECT EMPNO, ENAME, SAL, DEPTNO FROM EMP
WHERE JOB = :job_title;
Notice how the INSERT statement uses the subquery to obtain intermediate results.
You use the UPDATE statement to change the values of specified columns in a table or view. In the following example, you update the SAL and COMM columns in the EMP table:
EXEC SQL UPDATE EMP
SET SAL = :salary, COMM = :commission
WHERE EMPNO = :emp_number;
You can use the optional WHERE clause to specify the conditions under which rows are updated. See "Using the WHERE Clause" .
The SET clause lists the names of one or more columns for which you must provide values. You can use a subquery to provide the values, as the following example shows:
EXEC SQL UPDATE EMP
SET SAL = (SELECT AVG(SAL)*1.1 FROM EMP WHERE DEPTNO = 20)
WHERE EMPNO = :emp_number;
You use the DELETE statement to remove rows from a table or view. In the following example, you delete all employees in a given department from the EMP table:
EXEC SQL DELETE FROM EMP
WHERE DEPTNO = :dept_number;
You can use the optional WHERE clause to specify the condition under which rows are deleted.
You use the WHERE clause to select, update, or delete only those rows in a table or view that meet your search condition. The WHERE-clause search condition is a Boolean expression, which can include scalar host variables, host arrays (not in SELECT statements), and subqueries.
If you omit the WHERE clause, all rows in the table or view are processed. If you omit the WHERE clause in an UPDATE or DELETE statement, Oracle sets SQLWARN(5) in the SQLCA to 'W' to warn that all rows were processed.
When a query returns multiple rows, you can explicitly define a cursor to
A cursor identifies the current row in the set of rows returned by the query. This allows your program to process the rows one at a time. The following statements let you define and manipulate a cursor:
First you use the DECLARE statement to name the cursor and associate it with a query.
The OPEN statement executes the query and identifies all the rows that meet the query search condition. These rows form a set called the active set of the cursor. After opening the cursor, you can use it to retrieve the rows returned by its associated query.
Rows of the active set are retrieved one by one (unless you use host arrays). You use a FETCH statement to retrieve the current row in the active set. You can execute FETCH repeatedly until all rows have been retrieved.
When done fetching rows from the active set, you disable the cursor with a CLOSE statement, and the active set becomes undefined.
You use the DECLARE statement to define a cursor by giving it a name and associating it with a query, as the following example shows:
EXEC SQL DECLARE emp_cursor CURSOR FOR
SELECT ENAME, EMPNO, SAL
FROM EMP
WHERE DEPTNO = :dept_number;
The cursor name is an identifier used by the precompiler, not a host or program variable, and should not be defined in the Declare Section. Therefore, cursor names cannot be passed from one precompilation unit to another. Also, cursor names cannot be hyphenated. They can be any length, but only the first 31 characters are significant. For ANSI compatibility, use cursor names no longer than 18 characters.
The SELECT statement associated with the cursor cannot include an INTO clause. Rather, the INTO clause and list of output host variables are part of the FETCH statement.
Because it is declarative, the DECLARE statement must physically (not just logically) precede all other SQL statements referencing the cursor. That is, forward references to the cursor are not allowed. In the following example, the OPEN statement is misplaced:
EXEC SQL OPEN emp_cursor; -- misplaced OPEN statement
EXEC SQL DECLARE emp_cursor CURSOR FOR
SELECT ENAME, EMPNO, SAL
FROM EMP
WHERE ENAME = :emp_name;
The cursor control statements (DECLARE, OPEN, FETCH, CLOSE) must all occur within the same precompiled unit. For example, you cannot declare a cursor in file A, then open it in file B.
Your host program can declare as many cursors as it needs. However, in a given file, every DECLARE statement must be unique. That is, you cannot declare two cursors with the same name in one precompilation unit, even across blocks or procedures, because the scope of a cursor is global within a file. If you will be using many cursors, you might want to specify the MAXOPENCURSORS option. For more information about MAXOPENCURSORS, see page 6 - 28.
Use the OPEN statement to execute the query and identify the active set. In the following example, a cursor named emp_cursor is opened.
EXEC SQL OPEN emp_cursor;
OPEN positions the cursor just before the first row of the active set. It also zeroes the rows-processed count kept by SQLERRD(3) in the SQLCA. However, none of the rows is actually retrieved at this point. That will be done by the FETCH statement.
Once you open a cursor, the query's input host variables are not reexamined until you reopen the cursor. Thus, the active set does not change. To change the active set, you must reopen the cursor.
Generally, you should close a cursor before reopening it. However, if you specify MODE=ORACLE (the default), you need not close a cursor before reopening it. This can boost performance; for details, see Appendix C, "Performance Tuning."
The amount of work done by OPEN depends on the values of three precompiler options: HOLD_CURSOR, RELEASE_CURSOR, and MAXOPENCURSORS. For more information, see "Using the Precompiler Options" .
You use the FETCH statement to retrieve rows from the active set and specify the output host variables that will contain the results. Recall that the SELECT statement associated with the cursor cannot include an INTO clause. Rather, the INTO clause and list of output host variables are part of the FETCH statement. In the following example, you fetch into three host variables:
EXEC SQL FETCH emp_cursor
INTO :emp_name, :emp_number, :salary;
The cursor must have been previously declared and opened. The first time you execute FETCH, the cursor moves from before the first row in the active set to the first row. This row becomes the current row. Each subsequent execution of FETCH advances the cursor to the next row in the active set, changing the current row. The cursor can only move forward in the active set. To return to a row that has already been fetched, you must reopen the cursor, then begin again at the first row of the active set.
If you want to change the active set, you must assign new values to the input host variables in the query associated with the cursor, then reopen the cursor. When MODE={ANSI | ANSI14 | ANSI13}, you must close the cursor before reopening it.
As the next example shows, you can fetch from the same cursor using different sets of output host variables. However, corresponding host variables in the INTO clause of each FETCH statement must have the same datatype.
EXEC SQL DECLARE emp_cursor CURSOR FOR
SELECT ENAME, SAL FROM EMP WHERE DEPTNO = 20;
...
EXEC SQL OPEN emp_cursor;
EXEC SQL WHENEVER NOT FOUND DO ...
LOOP
EXEC SQL FETCH emp_cursor INTO :emp_name1, :salary1;
EXEC SQL FETCH emp_cursor INTO :emp_name2, :salary2;
EXEC SQL FETCH emp_cursor INTO :emp_name3, :salary3;
...
ENDLOOP;
If the active set is empty or contains no more rows, FETCH returns the "no data found" Oracle warning code to SQLCODE in the SQLCA (or when MODE=ANSI, to the status variable SQLSTATE). The status of the output host variables is indeterminate. (In a typical program, the WHENEVER NOT FOUND statement detects this error.) To reuse the cursor, you must reopen it.
When finished fetching rows from the active set, you close the cursor to free the resources, such as storage, acquired by opening the cursor. When a cursor is closed, parse locks are released. What resources are freed depends on how you specify the options HOLD_CURSOR and RELEASE_CURSOR. In the following example, you close the cursor named emp_cursor:
EXEC SQL CLOSE emp_cursor;
You cannot fetch from a closed cursor because its active set becomes undefined. If necessary, you can reopen a cursor (with new values for the input host variables, for example).
When MODE={ANSI13|ORACLE}, issuing a commit or rollback closes cursors referenced in a CURRENT OF clause. Other cursors are unaffected by a commit or rollback and if open, remain open. However, when MODE={ANSI|ANSI14}, issuing a commit or rollback closes all explicit cursors.
You use the CURRENT OF cursor_name clause in a DELETE or UPDATE statement to refer to the latest row fetched from the named cursor. The cursor must be open and positioned on a row. If no fetch has been done or if the cursor is not open, the CURRENT OF clause results in an error and processes no rows.
The FOR UPDATE OF clause is optional when you declare a cursor that is referenced in the CURRENT OF clause of an UPDATE or DELETE statement. The CURRENT OF clause signals the precompiler to add a FOR UPDATE clause if necessary. For more information, see "Using the FOR UPDATE OF Clause" .
In the following example, you use the CURRENT OF clause to refer to the latest row fetched from a cursor named emp_cursor:
EXEC SQL DECLARE emp_cursor CURSOR FOR
SELECT ENAME, SAL FROM EMP WHERE JOB = 'CLERK'
FOR UPDATE OF SAL;
...
EXEC SQL OPEN emp_cursor;
EXEC SQL WHENEVER NOT FOUND DO ...
LOOP
EXEC SQL FETCH emp_cursor INTO :emp_name, :salary;
...
EXEC SQL UPDATE EMP SET SAL = :new_salary
WHERE CURRENT OF emp_cursor;
ENDLOOP;
An explicit FOR UPDATE OF or an implicit FOR UPDATE acquires exclusive row locks. All rows are locked at the open, not as they are fetched, and are released when you commit or rollback. If you try to fetch from a FOR UPDATE cursor after a commit, Oracle generates the following error:
ORA-01002: fetch out of sequence
You cannot use host arrays with the CURRENT OF clause. For an alternative, see "Mimicking CURRENT OF" . Also, you cannot reference multiple tables in an associated FOR UPDATE OF clause, which means that you cannot do joins with the CURRENT OF clause. Finally, you cannot use the CURRENT OF clause in dynamic SQL.
The following example shows the typical sequence of cursor control statements in an application program:
-- Define a cursor.
EXEC SQL DECLARE emp_cursor CURSOR FOR
SELECT ENAME, JOB FROM EMP
WHERE EMPNO = :emp_number
FOR UPDATE OF JOB;
-- Open the cursor and identify the active set.
EXEC SQL OPEN emp_cursor;
-- Exit if the last row was already fetched.
EXEC SQL WHENEVER NOT FOUND DO no_more;
-- Fetch and process data in a loop.
LOOP
EXEC SQL FETCH emp_cursor INTO :emp_name, :job_title;
-- host-language statements that operate on the fetched data
EXEC SQL UPDATE EMP
SET JOB = :new_job_title
WHERE CURRENT OF emp_cursor;
ENDLOOP;
...
ROUTINE no_more
BEGIN
-- Disable the cursor.
EXEC SQL CLOSE emp_cursor;
EXEC SQL COMMIT WORK RELEASE;
exit program;
END no_more;
The following program illustrates the use of a cursor and the FETCH statement. The program prompts for a department number, then displays the names of all employees in that department.
All fetches except the final one return a row and, if no errors were detected during the fetch, a success status code. The final fetch fails and returns the "no data found" Oracle warning code to SQLCODE in the SQLCA. The cumulative number of rows actually fetched is found in SQLERRD(3) in the SQLCA.
-- declare host variables
EXEC SQL BEGIN DECLARE SECTION;
username CHARACTER(20);
password CHARACTER(20);
emp_name CHARACTER(10);
dept_number INTEGER;
EXEC SQL END DECLARE SECTION;
-- copy in the SQL Communications Area
EXEC SQL INCLUDE SQLCA;
display 'Username? ';
read username;
display 'Password? ';
read password;
-- handle processing errors
EXEC SQL WHENEVER SQLERROR DO sql_error;
-- log on to Oracle
EXEC SQL CONNECT :username IDENTIFIED BY :password;
display 'Connected to Oracle';
-- declare a cursor
EXEC SQL DECLARE emp_cursor CURSOR FOR
SELECT ENAME FROM EMP WHERE DEPTNO = :dept_number;
display 'Department number? ';
read dept_number;
-- open the cursor and identify the active set
EXEC SQL OPEN emp_cursor;
-- exit if the last row was already fetched
EXEC SQL WHENEVER NOT FOUND DO no_more;
display 'Employee Name';
display '-------------';
-- fetch and process data in a loop
LOOP
EXEC SQL FETCH emp_cursor INTO :emp_name; display emp_name;
ENDLOOP;
ROUTINE no_more
BEGIN
EXEC SQL CLOSE emp_cursor;
EXEC SQL COMMIT WORK RELEASE;
display 'End of program';
exit program;
END no_more;
ROUTINE sql_error
BEGIN
EXEC SQL WHENEVER SQLERROR CONTINUE;
EXEC SQL ROLLBACK WORK RELEASE;
display 'Processing error';
exit program with an error;
END sql_error;
This section gives a brief overview of cursor variables. For more information, see your host language supplement and the PL/SQL User's Guide and Reference.
When using static embedded SQL with the Pro*COBOL and Pro*FORTRAN Precompilers, you can declare cursor variables. Like a cursor, a cursor variable points to the current row in the active set of a multi-row query. Cursors differ from cursor variables the way constants differ from variables. While a cursor is static, a cursor variable is dynamic, because it is not tied to a specific query. You can open a cursor variable for any type-compatible query.
Also, you can assign new values to a cursor variable and pass it as a parameter to subprograms, including subprograms stored in an Oracle database. This gives you a convenient way to centralize data retrieval.
First, you declare the cursor variable. After declaring the variable, you use four statements to control a cursor variable:
After you declare the cursor variable and allocate memory for it, you must pass it as an input host variable (bind variable) to PL/SQL, OPEN it FOR a multi-row query on the server side, FETCH from it on the client side, then CLOSE it on either side.
How you declare a cursor variable is dependent on your host language. For instructions about declaring a cursor variable, see your host-language supplement.
You use the ALLOCATE statement to allocate memory for the cursor variable. The syntax follows:
EXEC SQL ALLOCATE <cursor_variable>;
You use the OPEN ... FOR statement to associate a cursor variable with a multi-row query, execute the query, and identify the active set. The syntax follows:
EXEC SQL OPEN <cursor_variable> FOR <select_statement>;
The SELECT statement can reference input host variables and PL/SQL variables, parameters, and functions but cannot be FOR UPDATE. In the following example, you open a cursor variable named emp_cv:
EXEC SQL OPEN emp_cv FOR SELECT * FROM EMP;
You must open a cursor variable on the server side. You do that by passing it as an input host variable to an anonymous PL/SQL block. At run time, the block is sent to the Oracle Server for execution. In the following example, you declare and initialize a cursor variable, then pass it to a PL/SQL block, which opens the cursor variable:
EXEC SQL BEGIN DECLARE SECTION;
...
-- declare cursor variable
emp_cur SQL_CURSOR;
EXEC SQL END DECLARE SECTION;
-- initialize cursor variable
EXEC SQL ALLOCATE :emp_cur;
EXEC SQL EXECUTE
-- pass cursor variable to PL/SQL block
BEGIN
-- open cursor variable
OPEN :emp_cur FOR SELECT * FROM EMP;
END;
END-EXEC;
Generally, you pass a cursor variable to PL/SQL by calling a stored procedure that declares a cursor variable as one of its formal parameters. For example, the following packaged procedure opens a cursor variable named emp_cv:
CREATE PACKAGE emp_data AS
-- define REF CURSOR type
TYPE EmpCurTyp IS REF CURSOR RETURN emp%ROWTYPE;
-- declare formal paramter of that type
PROCEDURE open_emp_cv (emp_cv IN OUT EmpCurTyp);
END emp_data;
CREATE PACKAGE BODY emp_data AS
PROCEDURE open_emp_cv (emp_cv IN OUT EmpCurTyp) IS
BEGIN
-- open cursor variable
OPEN emp_cv FOR SELECT * FROM emp;
END open_emp_cv;
END emp_data;
You can call the procedure from any application, as follows:
EXEC SQL EXECUTE
BEGIN
emp_data.open_emp_cv(:emp_cur);
END;
END-EXEC;
After opening a cursor variable for a multi-row query, you use the FETCH statement to retrieve rows from the active set one at a time. The syntax follows:
EXEC SQL FETCH cursor_variable_name
INTO {record_name | variable_name[, variable_name, ...]};
Each column value returned by the cursor variable is assigned to a corresponding field or variable in the INTO clause, providing their datatypes are compatible.
The FETCH statement must be executed on the client side. In the following example, you fetch rows into a host record named emp_rec:
-- exit loop when done fetching EXEC SQL WHENEVER NOT FOUND DO no_more; LOOP -- fetch row into record EXEC SQL FETCH :emp_cur INTO :emp_rec; -- process the data ENDLOOP;
You use the CLOSE statement to close a cursor variable, at which point its active set becomes undefined. The syntax follows:
EXEC SQL CLOSE cursor_variable_name;
The CLOSE statement can be executed on the client side or the server side. In the following example, when the last row is processed, you close the cursor variable emp_cur:
-- close cursor variable EXEC SQL CLOSE :emp_cur;
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