vault backup: 2024-05-18 00:07:35

Affected files: content/.obsidian/plugins/recent-files-obsidian/data.json content/.obsidian/workspace.json content/postgresql/PostgreSQL Constraint and Key.md content/postgresql/PostgreSQL Constraints.md content/postgresql/PostgreSQL Primary Key and Foreign Key.md content/postgresql/PostgreSQL Sequence and UUID.md content/postgresql/PostgreSQL Table.md content/postgresql/PostgreSQL.md
windsuzu · May 17, 2024 · 19bafd2 · 19bafd2
1 parent 2701aef
commit 19bafd2
Show file tree

Hide file tree

Showing 8 changed files with 147 additions and 90 deletions.
diff --git a/content/.obsidian/plugins/recent-files-obsidian/data.json b/content/.obsidian/plugins/recent-files-obsidian/data.json
@@ -1,32 +1,36 @@
 {
   "recentFiles": [
     {
-      "basename": "PostgreSQL",
-      "path": "postgresql/PostgreSQL.md"
+      "basename": "PostgreSQL Sequence and UUID",
+      "path": "postgresql/PostgreSQL Sequence and UUID.md"
     },
     {
-      "basename": "PostgreSQL Constraint and Key",
-      "path": "postgresql/PostgreSQL Constraint and Key.md"
+      "basename": "PostgreSQL",
+      "path": "postgresql/PostgreSQL.md"
     },
     {
-      "basename": "PostgreSQL Table",
-      "path": "postgresql/PostgreSQL Table.md"
+      "basename": "PostgreSQL Join",
+      "path": "postgresql/PostgreSQL Join.md"
     },
     {
       "basename": "PostgreSQL Delete",
       "path": "postgresql/PostgreSQL Delete.md"
     },
-    {
-      "basename": "PostgreSQL Join",
-      "path": "postgresql/PostgreSQL Join.md"
-    },
     {
       "basename": "PostgreSQL Update",
       "path": "postgresql/PostgreSQL Update.md"
     },
     {
-      "basename": "PostgreSQL Sequence and UUID",
-      "path": "postgresql/PostgreSQL Sequence and UUID.md"
+      "basename": "PostgreSQL Constraints",
+      "path": "postgresql/PostgreSQL Constraints.md"
+    },
+    {
+      "basename": "PostgreSQL Primary Key and Foreign Key",
+      "path": "postgresql/PostgreSQL Primary Key and Foreign Key.md"
+    },
+    {
+      "basename": "PostgreSQL Table",
+      "path": "postgresql/PostgreSQL Table.md"
     },
     {
       "basename": "PostgreSQL Database",
@@ -195,10 +199,6 @@
     {
       "basename": "The most ... in or of",
       "path": "english-grammar/The most ... in or of.md"
-    },
-    {
-      "basename": "Anymore vs Any more",
-      "path": "english-grammar/Anymore vs Any more.md"
     }
   ],
   "omittedPaths": [],

diff --git a/content/.obsidian/workspace.json b/content/.obsidian/workspace.json
@@ -13,31 +13,31 @@
             "state": {
               "type": "markdown",
               "state": {
-                "file": "postgresql/PostgreSQL.md",
+                "file": "postgresql/PostgreSQL Sequence and UUID.md",
                 "mode": "source",
                 "source": false
               }
             }
           },
           {
-            "id": "96a9372e3b208e7f",
+            "id": "fbaa50145f527248",
             "type": "leaf",
             "state": {
               "type": "markdown",
               "state": {
-                "file": "postgresql/PostgreSQL Constraint and Key.md",
+                "file": "postgresql/PostgreSQL Primary Key and Foreign Key.md",
                 "mode": "source",
                 "source": false
               }
             }
           },
           {
-            "id": "479dfa44c76beee2",
+            "id": "2592231430c39d6e",
             "type": "leaf",
             "state": {
               "type": "markdown",
               "state": {
-                "file": "postgresql/PostgreSQL Table.md",
+                "file": "postgresql/PostgreSQL Constraints.md",
                 "mode": "source",
                 "source": false
               }
@@ -126,7 +126,7 @@
             "state": {
               "type": "localgraph",
               "state": {
-                "file": "postgresql/PostgreSQL.md",
+                "file": "postgresql/PostgreSQL Sequence and UUID.md",
                 "options": {
                   "collapse-filter": true,
                   "search": "",
@@ -176,7 +176,7 @@
             "state": {
               "type": "outline",
               "state": {
-                "file": "postgresql/PostgreSQL.md"
+                "file": "postgresql/PostgreSQL Sequence and UUID.md"
               }
             }
           },
@@ -217,7 +217,7 @@
             "state": {
               "type": "file-properties",
               "state": {
-                "file": "postgresql/PostgreSQL.md"
+                "file": "postgresql/PostgreSQL Sequence and UUID.md"
               }
             }
           },
@@ -227,7 +227,7 @@
             "state": {
               "type": "backlink",
               "state": {
-                "file": "postgresql/PostgreSQL.md",
+                "file": "postgresql/PostgreSQL Sequence and UUID.md",
                 "collapseAll": false,
                 "extraContext": false,
                 "sortOrder": "alphabetical",
@@ -244,7 +244,7 @@
             "state": {
               "type": "outgoing-link",
               "state": {
-                "file": "postgresql/PostgreSQL.md",
+                "file": "postgresql/PostgreSQL Sequence and UUID.md",
                 "linksCollapsed": false,
                 "unlinkedCollapsed": false
               }
@@ -272,13 +272,14 @@
   },
   "active": "89b49aba37ae8848",
   "lastOpenFiles": [
-    "postgresql/PostgreSQL Constraint and Key.md",
-    "postgresql/PostgreSQL Table.md",
     "postgresql/PostgreSQL.md",
-    "postgresql/PostgreSQL Delete.md",
     "postgresql/PostgreSQL Join.md",
+    "postgresql/PostgreSQL Delete.md",
     "postgresql/PostgreSQL Update.md",
     "postgresql/PostgreSQL Sequence and UUID.md",
+    "postgresql/PostgreSQL Constraints.md",
+    "postgresql/PostgreSQL Primary Key and Foreign Key.md",
+    "postgresql/PostgreSQL Table.md",
     "postgresql/PostgreSQL Database.md",
     "postgresql/PostgreSQL Insert and Import.md",
     "postgresql/PostgreSQL Select.md",
@@ -299,7 +300,6 @@
     "mocs/CSS MOC.md",
     "mocs/React MOC.md",
     "mocs/Web-Dev MOC.md",
-    "mocs/JavaScript MOC.md",
     "fish-shell",
     "resume",
     "attachments/avatar-jay.jpeg",

diff --git a/content/postgresql/PostgreSQL Constraint and Key.md b/content/postgresql/PostgreSQL Constraint and Key.md
diff --git a/content/postgresql/PostgreSQL Constraints.md b/content/postgresql/PostgreSQL Constraints.md
@@ -0,0 +1,46 @@
+---
+draft: false
+date: 2024-05-17 23:32
+tags:
+  - postgres
+---
+
+Other than [[PostgreSQL Primary Key and Foreign Key|primary and foreign keys]], we can define constraints on any column during table creation (CREATE TABLE) or table modification (ALTER TABLE). These constraints can be forcing uniqueness or custom conditions.
+
+### NOT NULL
+
+```sql
+CREATE TABLE example (
+    name VARCHAR(100) NOT NULL
+);
+
+ALTER TABLE example ALTER COLUMN name SET NOT NULL;
+
+ALTER TABLE example ALTER COLUMN name DROP NOT NULL;
+```
+### UNIQUE
+
+```sql
+CREATE TABLE example (
+    email VARCHAR(150) UNIQUE
+);
+
+ALTER TABLE example ADD CONSTRAINT unique_email UNIQUE (email);
+ALTER TABLE example ADD UNIQUE (email);
+
+ALTER TABLE example DROP CONSTRAINT unique_email;
+```
+### CHECK
+
+```sql
+CREATE TABLE example (
+    age INT CHECK (age >= 18)
+);
+
+ALTER TABLE example ADD CONSTRAINT check_age CHECK (age >= 18);
+
+ALTER TABLE example DROP CONSTRAINT check_age;
+```
+
+> [!info] References
+> - [Learn PostgreSQL Tutorial - Full Course for Beginners (youtube.com)](https://www.youtube.com/watch?v=qw--VYLpxG4)
diff --git a/content/postgresql/PostgreSQL Primary Key and Foreign Key.md b/content/postgresql/PostgreSQL Primary Key and Foreign Key.md
@@ -0,0 +1,57 @@
+---
+draft: false
+date: 2024-05-17 23:14
+tags:
+  - postgres
+---
+
+### Primary Key
+
+We can assign a primary key to a single column or to a combination of columns, either when creating a table (`CREATE TABLE`) or when altering a table (`ALTER TABLE`).
+
+```sql
+CREATE TABLE person (
+	id BIGSERIAL PRIMARY KEY,
+	name VARCHAR(100)
+);
+
+CREATE TABLE person (
+	id BIGSERIAL,
+	name VARCHAR(100),
+	PRIMARY KEY (id, name)
+);
+
+ALTER TABLE person ADD PRIMARY KEY (id);
+ALTER TABLE person ADD PRIMARY KEY (id, name);
+```
+
+To remove a primary key from a table, you can use the `ALTER TABLE` statement to do it. Find the name of the primary key by using `\d table_name` before removing it.
+
+```sql
+ALTER TABLE person DROP CONSTRAINT person_pkey;
+```
+### Foreign Key
+
+We can create a relationship between two tables by using a foreign key from the child table to create a link to the primary key of the parent table. Creating a relationship between two tables can enable us to perform some useful commands, like `JOIN`, to [[PostgreSQL Join|join two tables]].
+
+```sql
+CREATE TABLE person (
+	id BIGSERIAL PRIMARY KEY,
+	name VARCHAR(100)
+);
+
+CREATE TABLE car (
+	id BIGSERIAL PRIMARY KEY,
+	person_id BIGINT,
+	FOREIGN KEY (person_id) REFERENCES person (id)	
+);
+```
+
+To remove a foreign key from a table, you can also use the `ALTER TABLE` statement do to it.
+
+```sql
+ALTER TABLE car DROP CONSTRAINT car_person_id_fkey;
+```
+
+> [!info] References
+> - [Learn PostgreSQL Tutorial - Full Course for Beginners (youtube.com)](https://www.youtube.com/watch?v=qw--VYLpxG4)
diff --git a/content/postgresql/PostgreSQL Sequence and UUID.md b/content/postgresql/PostgreSQL Sequence and UUID.md
@@ -1,14 +1,16 @@
 ---
 draft: false
-date: 2024-05-16 18:15
+date: 2024-05-17 23:37
 tags:
   - postgres
 ---
 
 ### BIGSERIAL
 
+The `BIGSERIAL` type assigns the column an auto-incrementing id starting at 1. If you want to restart the id number from a specific number, you can use `ALTER SEQUENCE` as the following statement.
+
 ```sql
-ALTER SEQUENCE person_id_seq RESTART WITH 0;
+ALTER SEQUENCE person_id_seq RESTART WITH 1;
 ```
 
 ### UUID

diff --git a/content/postgresql/PostgreSQL Table.md b/content/postgresql/PostgreSQL Table.md
@@ -1,6 +1,6 @@
 ---
 draft: false
-date: 2024-05-16 17:20
+date: 2024-05-17 21:54
 tags:
   - postgres
 ---
@@ -85,7 +85,10 @@ And use `\d table_name` to see the details of the specified table.
 
 ### Update a table
 
-To update a table, use `ALTER`. For example, you can update the column name by using `ALTER TABLE` with `RENAME TO`:
+To update a table, use `ALTER`. 
+#### Rename a column
+
+You can update the column name by using `ALTER TABLE` with `RENAME TO`:
 
 ```sql
 ALTER TABLE table_name RENAME column_name TO column_new_name;
@@ -94,6 +97,8 @@ ALTER TABLE person RENAME id TO person_uid;
 ALTER TABLE person RENAME gender TO sex;
 ```
 
+#### Update the data type
+
 Additionally, you can update the column type by using `ALTER TABLE` with `ALTER COLUMN` and `TYPE`:
 
 ```sql

diff --git a/content/postgresql/PostgreSQL.md b/content/postgresql/PostgreSQL.md
@@ -1,6 +1,6 @@
 ---
 draft: false
-date: 2024-05-16 18:18
+date: 2024-05-17 22:56
 tags:
   - postgres
 ---
@@ -14,7 +14,8 @@ tags:
 ## Table
 
 - [[PostgreSQL Table]]
-- [[PostgreSQL Constraint and Key]]
+- [[PostgreSQL Primary Key and Foreign Key]]
+- [[PostgreSQL Constraints]]
 - [[PostgreSQL Sequence and UUID]]
 
 ## Data Manipulation