SQL ALLOCATE

What is the purpose of the SQL ALLOCATE statement?

Reserves a cursor or SQL descriptor area at runtime in embedded or dynamic SQL.

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Compatible dialects for SQL ALLOCATE:

SQL ALLOCATE Full Explanation

SQL ALLOCATE is part of the SQL standard for embedded and dynamic SQL. It lets a program create resources during execution instead of at compile time. Two resources can be allocated:1. Cursor - ALLOCATE cursor_name CURSOR FOR statement_name binds a previously prepared statement to a new cursor handle.2. SQL Descriptor Area (SDA) - ALLOCATE DESCRIPTOR descriptor_name [WITH MAX n] creates a data structure that can hold column metadata and values when the number or types of columns are not known until runtime.After use, resources should be released with DEALLOCATE or FREE. ALLOCATE runs entirely on the client side of an embedded-SQL program; it does not return a result set, but the DBMS validates names and keeps metadata. Modern interactive SQL shells rarely expose ALLOCATE directly; it is mostly seen in host-language interfaces such as ECPG (PostgreSQL), IBM Db2 precompilers, and Oracle Pro*C.

SQL ALLOCATE Syntax

-- Allocate a cursor
ALLOCATE cursor_name CURSOR FOR statement_name;

-- Allocate a descriptor area
ALLOCATE DESCRIPTOR descriptor_name [WITH MAX {size | :host_var}];

SQL ALLOCATE Parameters

cursor_name (identifier) - Name of the cursor to create
statement_name (identifier) - Name of a prepared statement previously declared with PREPARE
descriptor_name (identifier) - Name of the SQL descriptor area to create
size (integer) - Maximum number of descriptor items (columns)
host_var (host var) - Host-language variable holding the maximum size

Example Queries Using SQL ALLOCATE

EXEC SQL PREPARE stmt1 FROM 'SELECT id, email FROM users WHERE active = 1';
EXEC SQL ALLOCATE cur1 CURSOR FOR stmt1;
EXEC SQL OPEN cur1;
EXEC SQL FETCH cur1 INTO :id, :email;
...
EXEC SQL DEALLOCATE cur1;

EXEC SQL ALLOCATE DESCRIPTOR dyn_desc WITH MAX 20;
EXEC SQL DESCRIBE OUTPUT stmt1 USING SQL DESCRIPTOR dyn_desc;

Expected Output Using SQL ALLOCATE

The cursor handle cur1 is now valid and can be opened, fetched, and closed
The descriptor dyn_desc exists in application memory and is filled by DESCRIBE OUTPUT
No result rows are returned by ALLOCATE itself

Use Cases with SQL ALLOCATE

Dynamic SQL when the exact number of cursors is unknown until runtime
Applications that must inspect column metadata without hard-coding it
Embedded SQL in C, COBOL, or PL/I programs that need late binding of statements
Drivers or middleware that build generic data-access layers

Common Mistakes with SQL ALLOCATE

Using ALLOCATE in interactive SQL shells that do not support embedded SQL
Forgetting to DEALLOCATE, leading to resource leaks
Assuming ALLOCATE automatically opens the cursor (OPEN is still required)
Omitting WITH MAX on DESCRIPTOR, causing runtime errors when too many columns are described
Mixing up descriptor allocation (client side) with temporary table creation (server side)

First Introduced In

SQL-92 Embedded SQL

Frequently Asked Questions

What is SQL ALLOCATE used for?

SQL ALLOCATE reserves a cursor or SQL descriptor area at runtime, letting an embedded SQL program handle dynamic SQL without static declarations.

Does ALLOCATE automatically open the cursor?

No. After allocating the cursor you must issue an OPEN statement before you can FETCH rows.

How do I release an allocated cursor or descriptor?

Issue DEALLOCATE (or FREE depending on dialect) once the resource is no longer required. This prevents memory or handle leaks.

Which databases recognize ALLOCATE?

It is available in IBM Db2, PostgreSQL ECPG, Oracle Pro*C, Informix ESQL/C, and other embedded SQL environments. MySQL, SQL Server, and SQLite do not support the keyword.