


Migrating from MySQL to PostgreSQL Key Query Differences and Considerations
Switching from MySQL to PostgreSQL requires careful consideration of query syntax, data types, and database features. This guide highlights key distinctions to facilitate a smooth migration process.
-
Data Type Mapping:
MySQL and PostgreSQL employ different data types. Here's a comparison:
MySQL Data Type | PostgreSQL Equivalent | Notes |
---|---|---|
TINYINT | SMALLINT | Use BOOLEAN for true/false. |
DATETIME | TIMESTAMP | Consider TIMESTAMPTZ for timezone awareness. |
TEXT | TEXT | Functionally identical. |
ENUM | TEXT CHECK constraint | PostgreSQL lacks ENUM; simulate using CHECK constraints. |
AUTO_INCREMENT | SERIAL or GENERATED AS IDENTITY | Use SERIAL or GENERATED AS IDENTITY for auto-incrementing keys. |
DOUBLE | DOUBLE PRECISION | Direct equivalent. |
BLOB | BYTEA | For binary large objects. |
-
Case Sensitivity in String Comparisons:
Case Sensitivity Differences:
-
MySQL:
LIKE
is case-insensitive by default (for non-binary columns). -
PostgreSQL:
LIKE
is case-sensitive; useILIKE
for case-insensitive matching.
Wildcards: Both databases use %
(zero or more characters) and _
(single character) wildcards.
Examples:
-
MySQL (case-insensitive):
SELECT * FROM users WHERE name LIKE 'john%';
-
PostgreSQL (case-insensitive equivalent):
SELECT * FROM users WHERE name ILIKE 'john%';
orSELECT * FROM users WHERE LOWER(name) LIKE 'john%';
Optimization: For efficient case-insensitive searches in PostgreSQL, create a functional index: CREATE INDEX idx_users_name_lower ON users (LOWER(name));
-
Auto-Incrementing Primary Keys:
-
MySQL: Uses
AUTO_INCREMENT
. -
PostgreSQL: Employs
SERIAL
orGENERATED AS IDENTITY
.
Examples:
-
MySQL:
CREATE TABLE users (id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR(100));
-
PostgreSQL:
CREATE TABLE users (id SERIAL PRIMARY KEY, name VARCHAR(100));
-
String Functions:
PostgreSQL's string function syntax may differ slightly from MySQL's.
MySQL Function | PostgreSQL Equivalent |
---|---|
CONCAT() | CONCAT() |
LENGTH() | LENGTH() |
SUBSTRING() | SUBSTRING() |
LOCATE() | POSITION() or STRPOS() |
REPLACE() | REPLACE() |
Example: Both databases use CONCAT()
identically: SELECT CONCAT(first_name, ' ', last_name) AS full_name FROM users;
-
Pagination (
LIMIT
andOFFSET
):
Both databases support LIMIT
and OFFSET
with identical syntax: SELECT * FROM users LIMIT 10 OFFSET 20;
-
Default Values:
PostgreSQL's default value handling is stricter.
-
MySQL:
CREATE TABLE orders (id INT AUTO_INCREMENT PRIMARY KEY, created_at DATETIME DEFAULT CURRENT_TIMESTAMP);
-
PostgreSQL:
CREATE TABLE orders (id SERIAL PRIMARY KEY, created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP);
-
Joins:
PostgreSQL enforces stricter SQL join standards. Ensure join columns have compatible data types or use explicit casting: SELECT * FROM orders JOIN customers ON orders.customer_id = customers.id::TEXT;
-
Full-Text Search:
-
MySQL: Uses
FULLTEXT
indexing. -
PostgreSQL: Leverages
TSVECTOR
andTSQUERY
for advanced full-text search.
Examples:
-
MySQL:
SELECT * FROM articles WHERE MATCH(content) AGAINST('search term');
-
PostgreSQL:
SELECT * FROM articles WHERE content @@ to_tsquery('search & term');
-
Foreign Key Constraints:
PostgreSQL enforces more rigorous foreign key constraints. Verify schema and data integrity.
-
Case Sensitivity of Identifiers:
- MySQL: Table and column names are generally case-insensitive (unless using a binary collation).
- PostgreSQL: Table and column names are case-sensitive when quoted ("table_name").
-
Stored Procedures:
Stored procedure syntax differs substantially.
-
MySQL: Uses
DELIMITER
to define procedures. -
PostgreSQL: Uses
DO
blocks orCREATE FUNCTION
.
-
Indexes:
PostgreSQL provides advanced indexing options (GIN, GiST, BRIN) and supports functional indexes.
Migration Strategy:
- Utilize migration tools like
pgLoader
or AWS DMS for automated schema and data transfer. - Manually review and adjust SQL queries, particularly those involving case sensitivity, auto-increment, full-text search, joins, and stored procedures.
- Optimize indexes for PostgreSQL's capabilities.
- Conduct thorough testing in a staging environment before production migration.
A thorough understanding of these differences ensures a successful and efficient migration from MySQL to PostgreSQL.
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