breaking(mysql): assume all non-binary collations compatible with str (#3924)

cc https://github.com/launchbadge/sqlx/pull/3400#issuecomment-3041035104

comment in `sqlx-mysql/src/collation.rs` for explanation

fixes #3200
fixes #3387
fixes #3390
fixes #3409

tests/mysql/macros.rs

@@ -555,4 +555,34 @@ async fn test_from_row_json_try_from_attr() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[cfg(all(mariadb, not(mariadb = "10_6"), feature = "time"))]
+#[sqlx_macros::test]
+async fn test_uuid_is_compatible_mariadb() -> anyhow::Result<()> {
+    use sqlx::types::time::OffsetDateTime;
+    use sqlx::types::Uuid;
+
+    struct Tweet {
+        id: Uuid,
+        text: String,
+        created_at: OffsetDateTime,
+        owner_id: Option<Uuid>,
+    }
+
+    let mut conn = new::<MySql>().await?;
+
+    sqlx::query!("INSERT INTO tweet_with_uuid(text) VALUES ('Hello, world!')")
+        .execute(&mut conn)
+        .await?;
+
+    let tweets: Vec<Tweet> = sqlx::query_as!(Tweet, "SELECT * FROM tweet_with_uuid")
+        .fetch_all(&mut conn)
+        .await?;
+
+    assert_eq!(tweets.len(), 1);
+
+    assert_eq!(tweets[0].text, "Hello, world!");
+
+    Ok(())
+}
+
 // we don't emit bind parameter type-checks for MySQL so testing the overrides is redundant

tests/mysql/mysql.rs

@@ -605,3 +605,34 @@ async fn select_statement_count(conn: &mut MySqlConnection) -> Result<i64, sqlx:
     .fetch_one(conn)
     .await
 }
+
+#[sqlx_macros::test]
+async fn issue_3200() -> anyhow::Result<()> {
+    let mut conn = new::<MySql>().await?;
+
+    sqlx::raw_sql(
+        "\
+        CREATE TABLE IF NOT EXISTS users
+        (
+            `id`                     BIGINT AUTO_INCREMENT,
+            `username`               VARCHAR(128) NOT NULL,
+            PRIMARY KEY (id)
+        );
+    ",
+    )
+    .execute(&mut conn)
+    .await?;
+
+    let result = sqlx::raw_sql(
+        "\
+        SET @myvar := 'test@test.com';
+        select id from users where username = @myvar;
+    ",
+    )
+    .fetch_optional(&mut conn)
+    .await?;
+
+    assert!(result.is_none(), "{result:?}");
+
+    Ok(())
+}

tests/mysql/setup-mariadb.sql

@@ -0,0 +1,10 @@
+-- additional SQL to execute for MariaDB databases
+
+CREATE TABLE tweet_with_uuid
+(
+    -- UUID is only a bespoke datatype in MariaDB.
+    id         UUID PRIMARY KEY   DEFAULT UUID(),
+    created_at TIMESTAMP NOT NULL DEFAULT NOW(),
+    text       TEXT      NOT NULL,
+    owner_id   UUID
+);