postgresql index:idx_name,length:5 can't work when AutoMigrate

postgresql index:idx_name,length:5 can't work when AutoMigrate gorm version v1.31.1 ``` SkuName string `json:"skuName" gorm:"column:sku_name;comment:skuName;index:idx_sku_name,length:10"` ``` it create normal index in log "CREATE INDEX IF NOT EXISTS \"idx_sku_name\" ON \"order\" (\"sku_name\")" but need sql like this CREATE INDEX idx_user_name ON "order" (LEFT(name, 5))