SQL PREPARE

What does the SQL PREPARE statement do?

Creates a named, parameterized statement that can be executed repeatedly with EXECUTE.

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Compatible dialects for SQL PREPARE: PostgreSQL, MySQL, MariaDB, SQL Server (sp_prepare), Oracle (using CURSOR variables), SQLite (C API), Snowflake

SQL PREPARE Full Explanation

SQL PREPARE defines a server-side prepared statement, giving it a name, optional parameter types, and the SQL command to run. The database parses, rewrites, and plans the statement once, then stores the execution plan in memory. Subsequent EXECUTE calls reference the prepared statement by name, supplying actual parameter values. This reduces parsing overhead, can improve performance, and guards against SQL-injection when used with parameters. Prepared statements live only for the current session unless explicitly DEALLOCATEd or the session ends. Some dialects (PostgreSQL, SQL Server with sp_prepare, MySQL with PREPARE … FROM) differ slightly in syntax and scope, but the core idea is identical: separate preparation from execution.

SQL PREPARE Syntax

-- PostgreSQL
PREPARE statement_name [ (data_type [, ...] ) ] AS
    sql_statement;

-- Execute later
EXECUTE statement_name [ (value [, ...] ) ];

-- Free resources
DEALLOCATE [ PREPARE ] statement_name;

SQL PREPARE Parameters

statement_name (identifier) - Name of the prepared statement (unique within the session)
data_type (type) - Optional list of parameter data types in positional order
sql_statement (string) - Any SQL command that can be parameterized (SELECT, INSERT, etc.)

Example Queries Using SQL PREPARE

-- 1. Prepare a parameterized SELECT
PREPARE get_orders (int) AS
  SELECT * FROM orders WHERE customer_id = $1;

-- 2. Use the prepared statement twice
EXECUTE get_orders(42);
EXECUTE get_orders(57);

-- 3. Clean up
DEALLOCATE get_orders;

Expected Output Using SQL PREPARE

PREPARE stores an execution plan named get_orders in the session
Each EXECUTE runs the plan with the supplied parameter, returning rows from orders
DEALLOCATE releases memory associated with the plan

Use Cases with SQL PREPARE

High-traffic services that run the same query many times with different inputs
Interactive sessions that loop over similar statements
Preventing SQL-injection by binding parameters instead of string-concatenating
Reducing latency in applications where parse and plan time is significant

Common Mistakes with SQL PREPARE

Forgetting to DEALLOCATE long-lived prepared statements, leading to session memory bloat
Mismatching the number or type of parameters between PREPARE and EXECUTE
Trying to prepare DDL commands that the dialect does not allow (e.g., CREATE TABLE)
Assuming prepared statements persist across sessions or connections

First Introduced In

PostgreSQL 7.3 (2002); later adopted by other DBMSs

Frequently Asked Questions

What benefits do prepared statements provide?

Prepared statements cut down repetitive parse and plan time, improve performance for frequently executed queries, and add a layer of SQL-injection protection by separating code from data.

Can I prepare any SQL command?

Most DML commands (SELECT, INSERT, UPDATE, DELETE) are supported. Some dialects disallow DDL like CREATE TABLE; consult your database docs.

How do I pass multiple parameters?

List parameter types in PREPARE, then supply values positionally in EXECUTE, for example EXECUTE my_stmt(10, 'active');

What happens if I EXECUTE after DEALLOCATE?

The database raises an error such as "prepared statement does not exist" because the cached plan has been removed.