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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minutePorting SQL between PostgreSQL and MySQL is not just a matter of replacing keywords. Identifier case, upsert behavior, generated values, and row counts can all change what your application does. The seven checks below are grounded in PostgreSQL 18 and MySQL Reference Manual 26.7; verify behavior against the exact server versions you deploy.
1. Identifier quotes and letter case
PostgreSQL uses double quotes to delimit identifiers. An unquoted name is folded to lowercase, while a quoted name preserves its case and must be referenced with matching case. For example, CREATE TABLE Customer creates the unquoted name customer, while CREATE TABLE "Customer" creates a case-sensitive identifier. See the PostgreSQL 18 identifier rules.
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During migration, inventory mixed-case names, reserved words, and identifiers with nonstandard characters, then check every DDL statement and query that refers to them. PostgreSQL advises choosing a consistent practice—always quote a particular name or never quote it—for portability. Do not assume MySQL interprets quotes the same way: its behavior is not established by the cited comparison sources, so check the target server’s configuration and documentation.
2. Upsert spelling and conflict selection
The engines use different clauses, but the important migration question is which uniqueness conflict triggers an update.
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| Engine | Clause | How the conflict is selected |
|---|---|---|
| PostgreSQL 18 | ON CONFLICT |
A conflict target can identify a unique index or constraint; DO UPDATE requires a conflict target. |
| MySQL Reference Manual 26.7 | ON DUPLICATE KEY UPDATE |
A duplicate value in a unique index or primary key triggers the update path. |
PostgreSQL’s INSERT reference and MySQL’s upsert reference describe these forms. A mechanical clause replacement can change which row is updated. Choose the intended conflict key for the destination engine and test the statement’s behavior under collisions.
3. Returning modified rows
PostgreSQL documents RETURNING for INSERT, UPDATE, DELETE, and MERGE. It can return generated defaults as well as other values from the modified row. An application that inserts a row and immediately consumes its returned fields may depend on more than just obtaining an auto-generated ID. See PostgreSQL’s RETURNING documentation.
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The cited MySQL generated-key guidance instead documents LAST_INSERT_ID() for retrieving the most recent AUTO_INCREMENT value. That does not make it a drop-in replacement for a returned row containing several columns. Rewrite and test the retrieval path for the target MySQL version, including any follow-up query needed to fetch other values; consult the MySQL AUTO_INCREMENT example.
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4. Generated integer column declarations
PostgreSQL documents serial and bigserial as autoincrementing types. MySQL’s documented form attaches the AUTO_INCREMENT attribute to an integer column. These declarations are not interchangeable DDL. See the PostgreSQL numeric types documentation and MySQL’s AUTO_INCREMENT example.
When translating a schema, verify the destination column’s integer type and range, its default and generation behavior, and how the application retrieves the generated value. These references cover the cited forms, not every identity-generation option supported by either product.
5. MySQL upsert affected-row counts
MySQL documents different affected-row values for INSERT ... ON DUPLICATE KEY UPDATE, depending on what happens:
- 1: a row is inserted.
- 2: an existing row is updated.
- 0: an existing row is assigned its current values.
The CLIENT_FOUND_ROWS connection flag changes the last case from 0 to 1. If application logic branches on a driver’s affected-row count, test each outcome using the actual client and connection settings. These figures describe MySQL’s documented behavior; the cited sources do not establish a PostgreSQL counterpart. See the MySQL upsert reference.
6. Upserts on tables with multiple unique indexes
MySQL warns against using ON DUPLICATE KEY UPDATE on tables with multiple unique indexes: a duplicate can match more than one row, and the statement may update only one of them. PostgreSQL’s explicit conflict target provides a different way to select the conflict handled by ON CONFLICT. See the MySQL upsert guidance and PostgreSQL’s INSERT reference.
For every migrated upsert, test collisions against each unique key, including cases where different keys match different existing rows. Confirm that the chosen row and resulting action match the application’s intended rule.
7. Proposed-row references and deprecated MySQL syntax
In PostgreSQL’s ON CONFLICT DO UPDATE form, excluded refers to the proposed row. MySQL’s ON DUPLICATE KEY UPDATE has its own syntax for referring to proposed values: the MySQL Reference Manual 26.7 marks VALUES(column) as deprecated and shows row or column aliases as the replacement pattern. Do not carry the deprecated form into new or migrated code without checking the deployed server’s supported syntax. See the PostgreSQL INSERT reference and MySQL’s upsert reference.
Is LIMIT or OFFSET a syntax difference?
No. PostgreSQL’s SELECT reference states that its LIMIT and OFFSET syntax is also used by MySQL. Those clauses are not one of the migration differences covered here.
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