diff --git a/migrations/dlu/mysql/29_dashboard_moderation.sql b/migrations/dlu/mysql/29_dashboard_moderation.sql
index a3a9f7669..48d25d322 100644
--- a/migrations/dlu/mysql/29_dashboard_moderation.sql
+++ b/migrations/dlu/mysql/29_dashboard_moderation.sql
@@ -1,6 +1,22 @@
-/* Columns used by the web dashboard. Names match NexusDashboard so databases it already migrated keep their data,
-   statements for columns that already exist fail individually and are skipped. */
-ALTER TABLE play_keys ADD COLUMN notes TEXT NULL;
-ALTER TABLE bug_reports ADD COLUMN resolved_time TIMESTAMP NULL DEFAULT NULL;
-ALTER TABLE bug_reports ADD COLUMN resoleved_by_id INT NULL;
-ALTER TABLE bug_reports ADD COLUMN resolution TEXT NULL;
+/* Columns used by the web dashboard. Names match NexusDashboard so databases it already migrated keep their data:
+   each column is only added when it is not there yet. */
+SET @dlu_column = (SELECT IF(COUNT(*) = 0, 'ALTER TABLE play_keys ADD COLUMN notes TEXT NULL', 'DO 0') FROM information_schema.columns
+	WHERE table_schema = DATABASE() AND table_name = 'play_keys' AND column_name = 'notes');
+PREPARE dlu_column_stmt FROM @dlu_column;
+EXECUTE dlu_column_stmt;
+DEALLOCATE PREPARE dlu_column_stmt;
+SET @dlu_column = (SELECT IF(COUNT(*) = 0, 'ALTER TABLE bug_reports ADD COLUMN resolved_time TIMESTAMP NULL DEFAULT NULL', 'DO 0') FROM information_schema.columns
+	WHERE table_schema = DATABASE() AND table_name = 'bug_reports' AND column_name = 'resolved_time');
+PREPARE dlu_column_stmt FROM @dlu_column;
+EXECUTE dlu_column_stmt;
+DEALLOCATE PREPARE dlu_column_stmt;
+SET @dlu_column = (SELECT IF(COUNT(*) = 0, 'ALTER TABLE bug_reports ADD COLUMN resoleved_by_id INT NULL', 'DO 0') FROM information_schema.columns
+	WHERE table_schema = DATABASE() AND table_name = 'bug_reports' AND column_name = 'resoleved_by_id');
+PREPARE dlu_column_stmt FROM @dlu_column;
+EXECUTE dlu_column_stmt;
+DEALLOCATE PREPARE dlu_column_stmt;
+SET @dlu_column = (SELECT IF(COUNT(*) = 0, 'ALTER TABLE bug_reports ADD COLUMN resolution TEXT NULL', 'DO 0') FROM information_schema.columns
+	WHERE table_schema = DATABASE() AND table_name = 'bug_reports' AND column_name = 'resolution');
+PREPARE dlu_column_stmt FROM @dlu_column;
+EXECUTE dlu_column_stmt;
+DEALLOCATE PREPARE dlu_column_stmt;
diff --git a/migrations/dlu/mysql/30_account_email.sql b/migrations/dlu/mysql/30_account_email.sql
index 1c141fa33..9909e90d1 100644
--- a/migrations/dlu/mysql/30_account_email.sql
+++ b/migrations/dlu/mysql/30_account_email.sql
@@ -1,7 +1,15 @@
-/* Account email for password resets. email/email_confirmed_at match NexusDashboard's columns so existing data is kept,
-   statements for columns that already exist fail individually and are skipped. */
-ALTER TABLE accounts ADD COLUMN email VARCHAR(255) NULL DEFAULT '';
-ALTER TABLE accounts ADD COLUMN email_confirmed_at DATETIME NULL DEFAULT NULL;
+/* Account email for password resets. email/email_confirmed_at match NexusDashboard's columns so existing data is kept:
+   they are only added when they are not there yet. */
+SET @dlu_column = (SELECT IF(COUNT(*) = 0, 'ALTER TABLE accounts ADD COLUMN email VARCHAR(255) NULL DEFAULT ''''', 'DO 0') FROM information_schema.columns
+	WHERE table_schema = DATABASE() AND table_name = 'accounts' AND column_name = 'email');
+PREPARE dlu_column_stmt FROM @dlu_column;
+EXECUTE dlu_column_stmt;
+DEALLOCATE PREPARE dlu_column_stmt;
+SET @dlu_column = (SELECT IF(COUNT(*) = 0, 'ALTER TABLE accounts ADD COLUMN email_confirmed_at DATETIME NULL DEFAULT NULL', 'DO 0') FROM information_schema.columns
+	WHERE table_schema = DATABASE() AND table_name = 'accounts' AND column_name = 'email_confirmed_at');
+PREPARE dlu_column_stmt FROM @dlu_column;
+EXECUTE dlu_column_stmt;
+DEALLOCATE PREPARE dlu_column_stmt;
 /* Sessions issued before this unix time are rejected, e.g. after a password reset */
 ALTER TABLE accounts ADD COLUMN sessions_valid_after BIGINT NOT NULL DEFAULT 0;
 CREATE TABLE IF NOT EXISTS account_tokens (
diff --git a/migrations/dlu/mysql/40_pet_name_owner.sql b/migrations/dlu/mysql/40_pet_name_owner.sql
index f49240ab6..cf76ad8b4 100644
--- a/migrations/dlu/mysql/40_pet_name_owner.sql
+++ b/migrations/dlu/mysql/40_pet_name_owner.sql
@@ -1,4 +1,17 @@
 /* Who owns each named pet, written by the game when the name is set. NULL: not looked up yet (the dashboard fills
    those in once from the characters' inventories); 0: no character has the pet any more. */
-ALTER TABLE pet_names ADD COLUMN owner_id BIGINT NULL DEFAULT NULL;
-CREATE INDEX pet_names_owner ON pet_names (owner_id);
+SET @dlu_column = (SELECT IF(COUNT(*) = 0, 'ALTER TABLE pet_names ADD COLUMN owner_id BIGINT NULL DEFAULT NULL', 'DO 0') FROM information_schema.columns
+	WHERE table_schema = DATABASE() AND table_name = 'pet_names' AND column_name = 'owner_id');
+PREPARE dlu_column_stmt FROM @dlu_column;
+EXECUTE dlu_column_stmt;
+DEALLOCATE PREPARE dlu_column_stmt;
+/* Some servers added this column (and an index on it) themselves: only index it when nothing does yet */
+SET @dlu_index = (SELECT IF(COUNT(*) = 0, 'CREATE INDEX pet_names_owner ON pet_names (owner_id)', 'DO 0') FROM information_schema.statistics
+	WHERE table_schema = DATABASE() AND table_name = 'pet_names' AND column_name = 'owner_id' AND seq_in_index = 1);
+PREPARE dlu_index_stmt FROM @dlu_index;
+EXECUTE dlu_index_stmt;
+DEALLOCATE PREPARE dlu_index_stmt;
+/* Those servers' character ids written before 23_store_character_id_as_objectid.sql, which did not convert this
+   column, have no persistent bit and match no character. Give them the bit, as 23 did for every other character id
+   column. Does nothing on a column just added (every row is NULL). */
+UPDATE pet_names SET owner_id = owner_id | 0x1000000000000000 WHERE owner_id > 0 AND owner_id < 0x1000000000000000;
diff --git a/migrations/dlu/mysql/57_lookup_indexes.sql b/migrations/dlu/mysql/57_lookup_indexes.sql
index d6aae3461..ae8349284 100644
--- a/migrations/dlu/mysql/57_lookup_indexes.sql
+++ b/migrations/dlu/mysql/57_lookup_indexes.sql
@@ -2,17 +2,51 @@
  * Indexes for lookups by owner/parent that otherwise scan the whole table: a property's models (and the model count
  * on every property list row), a character's properties, an account's characters, a play key's accounts, friends
  * both ways, a character's mail, a leaderboard's scores, and the dashboard's per-character/account related data.
- * The columns' inline REFERENCES clauses in 0_initial.sql create no foreign key (and so no index) in MySQL/MariaDB.
+ * Whether the columns' inline REFERENCES clauses in 0_initial.sql made a foreign key (and with it an index) depends on
+ * the server: MySQL before 9.0 ignores them, MariaDB 10.5 and later creates them. So each index on such a column is
+ * only created when no index starts with that column yet; a second one would only slow down writes.
  */
-CREATE INDEX properties_contents_property ON properties_contents (property_id);
-CREATE INDEX properties_contents_ugc ON properties_contents (ugc_id);
-CREATE INDEX properties_owner ON properties (owner_id);
-CREATE INDEX charinfo_account ON charinfo (account_id);
-CREATE INDEX accounts_play_key ON accounts (play_key_id);
-CREATE INDEX friends_friend ON friends (friend_id);
-CREATE INDEX mail_receiver ON mail (receiver_id);
+SET @dlu_index = (SELECT IF(COUNT(*) = 0, 'CREATE INDEX properties_contents_property ON properties_contents (property_id)', 'DO 0') FROM information_schema.statistics
+	WHERE table_schema = DATABASE() AND table_name = 'properties_contents' AND column_name = 'property_id' AND seq_in_index = 1);
+PREPARE dlu_index_stmt FROM @dlu_index;
+EXECUTE dlu_index_stmt;
+DEALLOCATE PREPARE dlu_index_stmt;
+SET @dlu_index = (SELECT IF(COUNT(*) = 0, 'CREATE INDEX properties_contents_ugc ON properties_contents (ugc_id)', 'DO 0') FROM information_schema.statistics
+	WHERE table_schema = DATABASE() AND table_name = 'properties_contents' AND column_name = 'ugc_id' AND seq_in_index = 1);
+PREPARE dlu_index_stmt FROM @dlu_index;
+EXECUTE dlu_index_stmt;
+DEALLOCATE PREPARE dlu_index_stmt;
+SET @dlu_index = (SELECT IF(COUNT(*) = 0, 'CREATE INDEX properties_owner ON properties (owner_id)', 'DO 0') FROM information_schema.statistics
+	WHERE table_schema = DATABASE() AND table_name = 'properties' AND column_name = 'owner_id' AND seq_in_index = 1);
+PREPARE dlu_index_stmt FROM @dlu_index;
+EXECUTE dlu_index_stmt;
+DEALLOCATE PREPARE dlu_index_stmt;
+SET @dlu_index = (SELECT IF(COUNT(*) = 0, 'CREATE INDEX charinfo_account ON charinfo (account_id)', 'DO 0') FROM information_schema.statistics
+	WHERE table_schema = DATABASE() AND table_name = 'charinfo' AND column_name = 'account_id' AND seq_in_index = 1);
+PREPARE dlu_index_stmt FROM @dlu_index;
+EXECUTE dlu_index_stmt;
+DEALLOCATE PREPARE dlu_index_stmt;
+SET @dlu_index = (SELECT IF(COUNT(*) = 0, 'CREATE INDEX accounts_play_key ON accounts (play_key_id)', 'DO 0') FROM information_schema.statistics
+	WHERE table_schema = DATABASE() AND table_name = 'accounts' AND column_name = 'play_key_id' AND seq_in_index = 1);
+PREPARE dlu_index_stmt FROM @dlu_index;
+EXECUTE dlu_index_stmt;
+DEALLOCATE PREPARE dlu_index_stmt;
+SET @dlu_index = (SELECT IF(COUNT(*) = 0, 'CREATE INDEX friends_friend ON friends (friend_id)', 'DO 0') FROM information_schema.statistics
+	WHERE table_schema = DATABASE() AND table_name = 'friends' AND column_name = 'friend_id' AND seq_in_index = 1);
+PREPARE dlu_index_stmt FROM @dlu_index;
+EXECUTE dlu_index_stmt;
+DEALLOCATE PREPARE dlu_index_stmt;
+SET @dlu_index = (SELECT IF(COUNT(*) = 0, 'CREATE INDEX mail_receiver ON mail (receiver_id)', 'DO 0') FROM information_schema.statistics
+	WHERE table_schema = DATABASE() AND table_name = 'mail' AND column_name = 'receiver_id' AND seq_in_index = 1);
+PREPARE dlu_index_stmt FROM @dlu_index;
+EXECUTE dlu_index_stmt;
+DEALLOCATE PREPARE dlu_index_stmt;
+SET @dlu_index = (SELECT IF(COUNT(*) = 0, 'CREATE INDEX player_cheat_detections_account ON player_cheat_detections (account_id)', 'DO 0') FROM information_schema.statistics
+	WHERE table_schema = DATABASE() AND table_name = 'player_cheat_detections' AND column_name = 'account_id' AND seq_in_index = 1);
+PREPARE dlu_index_stmt FROM @dlu_index;
+EXECUTE dlu_index_stmt;
+DEALLOCATE PREPARE dlu_index_stmt;
 CREATE INDEX leaderboard_game ON leaderboard (game_id, character_id);
 CREATE INDEX bug_reports_reporter ON bug_reports (reporter_id);
 CREATE INDEX economy_flags_character ON economy_flags (character_id, id);
-CREATE INDEX player_cheat_detections_account ON player_cheat_detections (account_id);
 CREATE INDEX chat_log_recipient ON chat_log (recipient_id);