[quinnj-bot]

On MariaDB, a DateTime parameter before 1970 or after 2106 is stored as NULL. There is no warning, even in strict mode. This affects prepared execute, execute(conn, sql, params), executemany, and MySQL.load of a DateTime column. MySQL is not affected.

Cause: DateTime parameters were sent as MYSQL_TYPE_TIMESTAMP, which was the 1.x mapping. MariaDB applies the TIMESTAMP range to a TIMESTAMP-typed parameter and turns values outside it into NULL, even when the target column is DATETIME. Timestamp{P} parameters already used MYSQL_TYPE_DATETIME and were correct.

Fix: bind DateTime as MYSQL_TYPE_DATETIME, the same as Timestamp.

Before (MariaDB 11.4.13 and 11.8.9, column DATETIME(3)):

prepared insert DateTime(1969,12,31,23,59,59), DateTime(1970,1,1,0,0,1), DateTime(2020,6,1,12,30,45,123), DateTime(2200,1,1), DateTime(1000,1,1)
  -> [NULL, 1970-01-01T00:00:01, 2020-06-01T12:30:45.123, NULL, NULL]
MySQL.load((id=[1, 2], born=[DateTime(1955,3,4), DateTime(1990,1,1)]), conn, "t")
  -> [NULL, 1990-01-01T00:00:00]

After: every value reads back unchanged on MariaDB 11.4.13, MariaDB 11.8.9, and MySQL 8.4.13.

Checks:

• TIMESTAMP columns store the same instant with either parameter type. I checked this on both servers with session time_zone = '+05:30', using UNIX_TIMESTAMP of the stored value.
• WHERE dt = ? with an out-of-range DateTime matched correctly before the fix, so only stored values were affected.
• New test in test/user_workflow.jl, which runs on both live lanes. It inserts DateTime values from 1955, 1969, and 2200 with executemany and with MySQL.load, then reads them back. Without the fix it fails 2 tests on MariaDB 11.4 and 11.8 (all three values read back missing). With the fix it passes on all three servers. The serverless signature test now expects MYSQL_TYPE_DATETIME.
• Full Pkg.test() locally on Julia 1.12.6, with Docker lanes mysql:8 (8.4.13) and mariadb:11.4, the integration tests, and the --trim=safe build: 2294/2294 passed.

Found by a differential comparison of MySQL.jl against PyMySQL and an independent binary-protocol decoder, on MySQL 8.4 and MariaDB 11.8. Every type was checked through text and binary, buffered and streaming paths. This was the only value mismatch.

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