diff --git a/dml/administrator.sql b/dml/administrator.sql
index 38ae67e..68f91d6 100644
--- a/dml/administrator.sql
+++ b/dml/administrator.sql
@@ -5,4 +5,4 @@ DML to create administrator testdata.
 */
 
 INSERT INTO administrator (administratorId, userId) VALUES
-  (NULL, (SELECT userId FROM user WHERE userName = "adm1337"));
\ No newline at end of file
+  (NULL, (SELECT userId FROM user WHERE userName = 'adm1337'));
\ No newline at end of file
diff --git a/dml/doctor.sql b/dml/doctor.sql
index 9e9b8fb..8ee8c4d 100644
--- a/dml/doctor.sql
+++ b/dml/doctor.sql
@@ -6,7 +6,7 @@ DML to create doctor testdata.
 */
 
 INSERT INTO doctor (doctorId, userId, calendarId, doctorIdSubstitute) VALUES
-  (NULL, (SELECT userId FROM user WHERE userName = "pta1234"), (select calendarId from calendar where calendarWorkingHoursIdMonday is not null and calendarWorkingHoursIdFriday is not null and calendarWorkingHoursIdTuesday is not null), NULL),
-  (NULL, (SELECT userId FROM user WHERE userName = "dru8472"), (select calendarId from calendar where calendarWorkingHoursIdMonday is null and calendarWorkingHoursIdFriday is null), NULL),
-  (NULL, (SELECT userId FROM user WHERE userName = "abc1234"), (select calendarId from calendar where calendarWorkingHoursIdTuesday is null and calendarWorkingHoursIdSaturday is null), NULL),
-  (NULL, (SELECT userId FROM user WHERE userName = "xyz7890"), (select calendarId from calendar where calendarWorkingHoursIdSaturday is not null), NULL);
+  (NULL, (SELECT userId FROM user WHERE userName = 'pta1234'), (select calendarId from calendar where calendarWorkingHoursIdMonday is not null and calendarWorkingHoursIdFriday is not null and calendarWorkingHoursIdTuesday is not null), NULL),
+  (NULL, (SELECT userId FROM user WHERE userName = 'dru8472'), (select calendarId from calendar where calendarWorkingHoursIdMonday is null and calendarWorkingHoursIdFriday is null), NULL),
+  (NULL, (SELECT userId FROM user WHERE userName = 'abc1234'), (select calendarId from calendar where calendarWorkingHoursIdTuesday is null and calendarWorkingHoursIdSaturday is null), NULL),
+  (NULL, (SELECT userId FROM user WHERE userName = 'xyz7890'), (select calendarId from calendar where calendarWorkingHoursIdSaturday is not null), NULL);
diff --git a/dml/orthoptist.sql b/dml/orthoptist.sql
index a56b84a..b3b2281 100644
--- a/dml/orthoptist.sql
+++ b/dml/orthoptist.sql
@@ -5,5 +5,5 @@ DML to create orthoptist testdata.
 */
 
 INSERT INTO orthoptist (orthoptistId, userId, calendarId) VALUES
-  (NULL, (SELECT userId FROM user WHERE userName = "ort1234"), NULL),
-  (NULL, (SELECT userId FROM user WHERE userName = "ort5678"), NULL);
\ No newline at end of file
+  (NULL, (SELECT userId FROM user WHERE userName = 'ort1234'), NULL),
+  (NULL, (SELECT userId FROM user WHERE userName = 'ort5678'), NULL);
\ No newline at end of file
diff --git a/dml/receptionist.sql b/dml/receptionist.sql
index 7997193..2c2ae43 100644
--- a/dml/receptionist.sql
+++ b/dml/receptionist.sql
@@ -5,4 +5,4 @@ DML to create receptionist testdata.
 */
 
 INSERT INTO receptionist (receptionistId, userId) VALUES
-  (NULL, (SELECT userId FROM user WHERE userName = "spr1357"));
\ No newline at end of file
+  (NULL, (SELECT userId FROM user WHERE userName = 'spr1357'));
\ No newline at end of file
diff --git a/dml/user.sql b/dml/user.sql
index b71204a..30e5e8d 100644
--- a/dml/user.sql
+++ b/dml/user.sql
@@ -5,11 +5,11 @@ DML to create user testdata.
 */
 
 INSERT INTO user (userId, userGroupId, userName, password, createDate, idleDate) VALUES
-  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = "Arzt"), "pta1234", "password", NULL, NULL),
-  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = "Arzt"), "dru8472", "password", NULL, NULL),
-  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = "Arzt"), "abc1234", "password", NULL, NULL),
-  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = "Arzt"), "xyz7890", "password", NULL, NULL),
-  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = "Orthoptist"), "ort1234", "password", NULL, NULL),
-  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = "Orthoptist"), "ort5678", "password", NULL, NULL),
-  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = "Sprechstundenhilfe"), "spr1357", "password", NULL, NULL),
-  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = "Administrator"), "adm1337", "password", NULL, NULL);
+  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = 'Arzt'), 'pta1234', 'password', NULL, NULL),
+  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = 'Arzt'), 'dru8472', 'password', NULL, NULL),
+  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = 'Arzt'), 'abc1234', 'password', NULL, NULL),
+  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = 'Arzt'), 'xyz7890', 'password', NULL, NULL),
+  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = 'Orthoptist'), 'ort1234', 'password', NULL, NULL),
+  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = 'Orthoptist'), 'ort5678', 'password', NULL, NULL),
+  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = 'Sprechstundenhilfe'), 'spr1357', 'password', NULL, NULL),
+  (NULL, (SELECT userGroupId FROM usergroup WHERE userGroupName = 'Administrator'), 'adm1337', 'password', NULL, NULL);