fix(server): MySQL index DDL and retention DELETE compatibility

Author: Cod-e-Codes

server/db_dialect.go

@@ -2,9 +2,12 @@ package server
 
 import (
 	"database/sql"
+	"errors"
 	"fmt"
 	"strings"
 	"sync"
+
+	mysqlerr "github.com/go-sql-driver/mysql"
 )
 
 type DBDialect string
@@ -120,3 +123,9 @@ func insertIgnoreReadReceiptSQL(db *sql.DB) string {
 func supportsLastInsertID(db *sql.DB) bool {
 	return getDBDialect(db) != DialectPostgres
 }
+
+// isMySQLDuplicateKeyName reports whether err is MySQL errno 1061 (index already exists).
+func isMySQLDuplicateKeyName(err error) bool {
+	var me *mysqlerr.MySQLError
+	return errors.As(err, &me) && me.Number == 1061
+}

server/handlers.go

@@ -253,8 +253,16 @@ func CreateSchema(db *sql.DB) {
 	}
 
 	for _, index := range indexes {
-		_, err = dbExec(db, index)
+		q := index
+		if dialect == DialectMySQL {
+			// MySQL does not support "CREATE INDEX IF NOT EXISTS ..." (syntax error).
+			q = strings.Replace(index, "IF NOT EXISTS ", "", 1)
+		}
+		_, err = dbExec(db, q)
 		if err != nil {
+			if dialect == DialectMySQL && isMySQLDuplicateKeyName(err) {
+				continue
+			}
 			log.Printf("Warning: failed to create index: %v", err)
 		}
 	}
@@ -429,8 +437,11 @@ func enforceMessageRetention(db *sql.DB) {
 
 	if ttl > 0 {
 		for {
+			// Nested subquery keeps MySQL happy (LIMIT inside IN/NOT IN is invalid otherwise).
 			result, err := dbExec(db, `DELETE FROM messages WHERE id IN (
-				SELECT id FROM messages WHERE created_at < ? ORDER BY id ASC LIMIT 500
+				SELECT id FROM (
+					SELECT id FROM messages WHERE created_at < ? ORDER BY id ASC LIMIT 500
+				) AS ttl_batch
 			)`, time.Now().Add(-ttl))
 			if err != nil {
 				log.Printf("Error enforcing TTL retention: %v", err)
@@ -443,7 +454,11 @@ func enforceMessageRetention(db *sql.DB) {
 		}
 	}
 
-	_, err := dbExec(db, `DELETE FROM messages WHERE id NOT IN (SELECT id FROM messages ORDER BY id DESC LIMIT ?)`, maxMessages)
+	_, err := dbExec(db, `DELETE FROM messages WHERE id NOT IN (
+		SELECT id FROM (
+			SELECT id FROM messages ORDER BY id DESC LIMIT ?
+		) AS keep_batch
+	)`, maxMessages)
 	if err != nil {
 		log.Printf("Error enforcing message cap: %v", err)
 	}