This document summarizes an SQL DDL presentation covering IDs, domains, calculated columns, constraints, and triggers. It discusses various techniques for each topic, such as using sequences or auto-increment for IDs, domains for standardizing data types, views or generated columns for calculations, primary keys, foreign keys, unique constraints and checks for data integrity rules, and DML, DDL, and database triggers for logging and validation. The presentation provides pros and cons of each approach and concludes that thinking low-level and writing high-level code are important principles for working with SQL DDL.

1. SQL DDL: tricks and tips
Java Professionals Meetup #27, Minsk, 24th September 2019
Mikalai Sitsko

2. A. Contents
I. Introduction
II. SQL DDL (Data Definition Language)
1. IDs
2. Domains
3. Calculated Columns
4. Constraints
5. Triggers
III. Q&A
2

3. Short summary
3

4. RDBMS Ranks
https://db-engines.com/en/ranking
4

5. DB History (brief)
1960s
CODASYL
(network)
IMS
(hierarchical)
1970s
E.F. Codd
(Relation model)
P. Chen
(E-R),
RDBMS
1980s
J. Gray
(ACID)
SQL
client-server RDBMS
file-server DBMS
1990s 2000s
Web
commerce
E. Brewer
(BASE/CAP)
NoSQL
2010s
Cloud
BigData
Timeseries
Temporal
5

6. SQL is not dead!
Long-Life Secret
• Standard
• Evolution
• Declarative
• Implementation
6

7. II. DDL (Data Definition Language)
7

8. ID (identification)
Problem: How to generate a new ID ?
8

9. ID (#1 uuid)
9
Cons:
- Oversize
- Hard remember
- Non ordered
498e07d6-6c93-4519-b463-c904d6321af5
Pros:
+ Concurrency/parallel
+ RDBMS/backend

10. ID (#1 uuid)
-- DML
INSERT INTO person (id, …)
VALUES(NEWID(),…)
10
-- DDL
CREATE TABLE person (
id uniqueidentifier,
…)

11. ID (#2 generator table)
11
Cons:
- slow
- pessimistic lock
Pros:
+ ?

12. ID (#3 MAX+1)
12
newId = MAX(id)+1
Cons:
- slow
- pessimistic lock
Pros:
+ ?

13. 13
-- DML
SELECT
COALESCE(MAX(id), 0) + 1
FROM person
INTO :pId
WITH LOCK;
INSERT INTO PERSON(id,…) VALUES(:pId,…);
ID (#3 MAX+1)

14. ID (#4 Autoincrement/IDENTITY)
14
Cons:
- Restrictions
- Before insert
Pros:
+ Simple
+ Fast

15. ID (#4 Autoincrement/IDENTITY)
-- DML
INSERT INTO person(first_name,…)
VALUES('name',…);
-- DDL
CREATE TABLE person (
id int IDENTITY NOT NULL PRIMARY KEY,
…)
15

16. ID (#5 Sequence)
16
Cons:
- ?
Pros:
+ Simple
+ Fast
+ RDBMS/Backend

17. ID (#5 Sequence)
-- DML
INSERT INTO PERSON(id, first_name,…)
VALUES(NEXT VALUE FOR seq_person,
'name', …);
-- DDL
CREATE SEQUENCE seq_person;
CREATE TABLE person (
id int NOT NULL PRIMARY KEY,
…);
17

18. ID (conclusion)
18
Possible solutions:
1. Sequence
2. Autoincrement/Identity
3. UUID
4. Generator tables
5. MAX(id) + 1

19. Domains
19
Antilia, Mumbai, India

20. Domains
20
-- DDL
CREATE DOMAIN d_street VARCHAR(64);
CREATE TABLE office( …
street d_street,
… );
Cons:
- ?
Pros:
+ Unified

21. Calculated Columns
21
Ancient Temple

22. Calculated Columns (#1 select)
-- DML
SELECT
p.last_name || ', ' || p.first_name,
…
FROM person p
22
Cons:
- Code duplication
Pros:
+ Simple

23. Calculated Columns (#2 view)
-- DDL
CREATE VIEW v_person AS
SELECT
p.last_name || ', ' || p.first_name AS full_name,
…
FROM person p
23
Cons:
- Views
Pros:
+ Deduplication

24. Calculated Columns (#3 generated)
-- DDL
ALTER TABLE person ADD
full_name GENERATED ALWAYS AS
p.last_name || ', ' || p.first_name;
-- DML
SELECT
p.full_name,
…
FROM person p
24
Cons:
- ?
Pros:
+ Deduplication
+ Fast

25. Calculated Columns (conclusion)
25
Possible solutions:
1. Generated column
2. View
3. Backend
4. Select

26. Constraints
26
Last hope

27. Constraints/Primary Key
-- DDL
CREATE TABLE person(
id int NOT NULL PRIMARY KEY,
…
);
27

28. Constraints/Primary Key
28
-- DDL
ALTER TABLE person
ADD CONSTRAINT pk_person PRIMARY KEY(id);
Cons:
- ?
Pros:
+ Name

29. Constraints/Foreign key
-- DDL
ALTER TABLE office ADD CONSTRAINT fk_office_person
FOREIGN KEY (person_id) REFERENCE person (id);
29

30. Constraints/Foreign key
-- DDL
ALTER TABLE office ADD CONSTRAINT
fk_office_person
FOREIGN KEY (person_id) REFERENCE person (id)
ON DELETE CASCADE ON UPDATE CASCADE;
Type of actions
---------------
NO ACTION
CASCADE
SET NULL
SET DEFAULT
30
Cons:
- ?
Pros:
+ Explicit actions
+ Faster than ORM
+ Consistency

31. Constraints/Checks
31
-- DDL
ALTER TABLE person
ADD CONSTRAINT chk_nick
CHECK(nick SIMILAR TO '[[:ALPHA:]]');
Cons:
- Slow persistence
Pros:
+ Consistency

32. Constraints/Unique
32
-- DDL
ALTER TABLE person ADD CONSTRAINT uq_nick UNIQUE (nick);
Cons:
- Slow persistence
Pros:
+ Consistency

33. Constraints (conclusion)
33
Constraint types:
------------
1.Primary key
2.Foreign key
3.Check
4.Unique

34. Triggers
34

35. DML Triggers
35
DML Triggers
-------------
- object: table, view
- action: insert/delete/update
- repeating: for each row/statement
- when: before/after/instead of
- values: old/new
- amount: multiple per action, order
- status: active/inactive
Cons:
- Slow bulk
- Complexity
Pros:
+ Faster than backend
+ Log
+ Security
+ Statistic

36. DDL&Database Triggers
36
DDL Triggers
----
- object: tables, views, procedures etc
- action: create/alter/drop etc
- status: active/inactive
Database Triggers
----
- object: database, transaction
- action: start/connect
- status: active/inactive
Cons:
- ?
Pros:
+ Log
+ Security

37. Triggers
37
Type of Triggers:
----------------
1. DML
2. DDL
3. Database

38. Conclusion
38
1.ID
2.Domains
3.Calculated Columns
4.Constraints
5.Triggers

39. First, Thinking Low-Level,
Second, Writing High-Level
39

40. www.andersenlab.com
Mikalai Sitsko
Developer
Telegram: @sitsko
+375 29 7514375
n.sitsko@andersenlab.com
Thanks,
any questions?