[RFC]: Document the MySQL >= 8.0.19 / PHP >= 8.3 support floor and cover ALTER TABLE drop paths with MySQL tests

[simon-mundy]

Proposed Version

Docs: 0.4.1 (0.4.x). CI and tests: 0.5.0 (0.5.x).

Basic Information

State a support floor of MySQL >= 8.0.19 and PHP >= 8.3, exercise the floor and the current LTS releases in CI, and add the adapter's first DDL tests — AlterTable drop paths and table options. One small docs PR in core corrects alter-drop.md and the "MySQL/MariaDB" wording.

Background

AlterTable::dropConstraint($name) renders DROP CONSTRAINT <name> (AlterTable.php#L74-L78, #L254-L262) and the MySQL AlterTableDecorator leaves it alone. MySQL supports that general form from 8.0.19 for any named constraint. Verified on 8.4.10 (reproduced on 8.0.46):

ALTER TABLE `t` DROP CONSTRAINT `fk_parent`   -- FOREIGN KEY: OK
ALTER TABLE `t` DROP CONSTRAINT `uq_email`    -- UNIQUE:      OK
ALTER TABLE `t` DROP CONSTRAINT `chk_age`     -- CHECK:       OK
ALTER TABLE `t` DROP CONSTRAINT `PRIMARY`     -- PRIMARY KEY: OK
ALTER TABLE `t` DROP CONSTRAINT `idx_name`    -- plain INDEX: ERROR 3940: Constraint 'idx_name' does not exist.
ALTER TABLE `t` DROP INDEX `idx_name`         -- via dropIndex(): OK

So the rendering is right for the versions we intend to support — but nothing says what those are:

• No MySQL version statement in the README or docs. Core docs go the other way and advertise "MySQL/MariaDB" (docs/book/index.md:20, docs/book/adapter.md:24).
• CI runs the floating mysql:8.0 image (.github/workflows/continuous-integration.yml) via the shared phpdb-qa-tools reusable workflow, which takes one db-image string and has no matrix. That image is a late 8.0.4x, so the floor is never exercised.
• Core docs/book/sql-ddl/alter-drop.md shows DROP CONSTRAINT as universal output and only warns about SQLite (advanced.md).
• test/unit/Sql/Ddl/AlterTableDecoratorTest.php covers column options only. dropConstraint(), dropIndex(), dropColumn() and table options have no adapter test, and there are no DDL integration tests at all — tables come from the raw mysql.sql fixture.
• PHP ~8.3.0 || ~8.4.0 || ~8.5.0 is in composer.json but not in the README either.

Considerations

• Name clashes. MySQL raises ERROR 3939 ("Table has multiple constraints with the name ... Please use constraint specific DROP clause") when a FOREIGN KEY shares its name with another constraint — UNIQUE or CHECK. A same-named plain index is not a conflict; MySQL drops the FK and leaves its auto-created index behind. In the 3939 case typed helpers (dropForeignKey(), dropCheck(), ...) are the only way out, and core cannot emit DROP FOREIGN KEY at all today. That is a core follow-up rather than part of this.
• Error assertions. InvalidQueryException carries no errno, so a test has to catch the driver exception: mysqli_sql_exception::getCode() === 3940, or for PDO getCode() === 'HY000' with errorInfo[1] === 3940.
• Table options. ENGINE and COMMENT take quoted strings; ALGORITHM and LOCK only work when passed as a Literal (a plain string renders ALGORITHM = 'INPLACE', which MySQL rejects with 1064). The tests pin the generic setOption() mechanism as it stands; typed keyword options are proposed in the core statements umbrella, [RFC]: DDL standalone index, view, rename and truncate statements, and typed table options phpdb#179.
• Images. As of September 2026 mysql:lts resolves to 9.7 and 8.4 is the previous LTS. One uses: job per image, since the reusable workflow only takes one. Untested assumption: a 2020-era mysql:8.0.19 image still boots and passes the fixture loader on current GitHub runners.
• MariaDB is out of scope and should be stated as untested.

Proposal(s)

1. README "Supported versions": MySQL >= 8.0.19, PHP >= 8.3. State that MariaDB is not tested.
2. CI: mysql:8.0.19 (the floor) plus mysql:8.4 and mysql:9.7 (current LTS releases), as three uses: jobs. mysql:innovation optional as an early-removal canary.
3. Adapter unit tests asserting exact rendered SQL for dropConstraint(), dropIndex(), dropColumn(), changeColumn() and the table options ENGINE, COMMENT, ALGORITHM (Literal), LOCK (Literal).
4. Integration test — the adapter's first for DDL: create a table with a FK, a UNIQUE, a CHECK, a PK and a plain index; drop each through dropConstraint(); assert success for the first four and driver error 3940 for the plain index; then drop it with dropIndex(). I have run the full scenario through AlterTableDecorator and it behaves as described.
5. Core docs PR: alter-drop.md notes the MySQL floor for DROP CONSTRAINT, points non-unique index drops at dropIndex(), and documents the 3939 clash; same PR drops the "MySQL/MariaDB" wording in index.md and adapter.md.

Test plan:

• README states the floor; CI has 8.0.19, 8.4 and 9.7 jobs, all green.
• AlterTableDecoratorTest has one test per drop kind and per table option, exact-string assertions.
• The integration test above passes on every CI image.
• Core alter-drop.md, index.md and adapter.md updated in a separate PR, linked here.

Appendix/Additional Info

• MySQL reference manual, ALTER TABLE: "As of MySQL 8.0.19, ALTER TABLE permits more general (and SQL standard) syntax for dropping and altering existing constraints of any type".
• From an internal DDL audit (not published — the SQL verification above is the relevant part).