SQL CAST and CONVERT: Change Data Types (All Databases)

Overview

CAST converts a value from one data type to another. It is the SQL standard way to change types and works in every database.

All Databases

-- CAST(expression AS type):
SELECT CAST('123' AS INT);           -- 123 (string to integer)
SELECT CAST(123 AS VARCHAR(10));      -- '123' (integer to string)
SELECT CAST('2026-03-12' AS DATE);    -- date object
SELECT CAST(99.99 AS INT);            -- 99 (truncates decimal)
SELECT CAST(price AS DECIMAL(10,2)) FROM products;

MySQL

-- CAST:
SELECT CAST('123' AS UNSIGNED);       -- 123
SELECT CAST('2026-03-12' AS DATE);    -- date
SELECT CAST(123 AS CHAR);             -- '123'

-- CONVERT (MySQL syntax — different from SQL Server!):
SELECT CONVERT('123', UNSIGNED);      -- 123
SELECT CONVERT('abc', BINARY);        -- binary

-- Implicit conversion:
SELECT '10' + 5;  -- 15 (MySQL auto-converts)

PostgreSQL

-- CAST:
SELECT CAST('123' AS INTEGER);        -- 123
SELECT CAST(NOW() AS DATE);            -- date only

-- :: shorthand (PostgreSQL only):
SELECT '123'::INTEGER;                 -- 123
SELECT '2026-03-12'::DATE;             -- date
SELECT 99.99::INT;                     -- 100 (rounds)
SELECT NOW()::DATE;                    -- today's date
SELECT '{"key": "value"}'::JSONB;     -- JSON object

SQL Server

-- CAST:
SELECT CAST('123' AS INT);             -- 123
SELECT CAST(GETDATE() AS DATE);        -- date only

-- CONVERT(type, expression, style):
SELECT CONVERT(INT, '123');             -- 123
SELECT CONVERT(VARCHAR, GETDATE(), 23); -- '2026-03-12'

-- TRY_CAST / TRY_CONVERT (safe, returns NULL on failure):
SELECT TRY_CAST('abc' AS INT);         -- NULL (not an error)
SELECT TRY_CONVERT(DATE, 'not-date');  -- NULL

Skip the Syntax Lookup

Instead of memorizing CAST / CONVERT syntax for each database, describe what you need in plain English and let AI2SQL generate the correct query.

Frequently Asked Questions