vault backup: 2024-05-16 11:48:03

Affected files: content/.obsidian/plugins/recent-files-obsidian/data.json content/.obsidian/workspace.json content/postgresql/PostgreSQL Insert and Import.md content/postgresql/PostgreSQL Select.md
windsuzu · May 16, 2024 · e55093c · e55093c
1 parent 1cde929
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diff --git a/content/.obsidian/plugins/recent-files-obsidian/data.json b/content/.obsidian/plugins/recent-files-obsidian/data.json
@@ -1,17 +1,25 @@
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-      "basename": "PostgreSQL Select",
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+      "basename": "Install PostgreSQL on WSL 2 (Ubuntu)",
+      "path": "postgresql/Install PostgreSQL on WSL 2 (Ubuntu).md"
     },
     {
       "basename": "PostgreSQL",
       "path": "postgresql/PostgreSQL.md"
     },
+    {
+      "basename": "PostgreSQL Select",
+      "path": "postgresql/PostgreSQL Select.md"
+    },
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       "basename": "PostgreSQL Insert and Import",
       "path": "postgresql/PostgreSQL Insert and Import.md"
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+    {
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+      "path": "postgresql/PostgreSQL Tables.md"
+    },
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       "path": "postgresql/PostgreSQL Databases.md"
@@ -20,14 +28,6 @@
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diff --git a/content/.obsidian/workspace.json b/content/.obsidian/workspace.json
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@@ -206,7 +193,7 @@
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@@ -233,7 +220,7 @@
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@@ -259,15 +246,15 @@
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+    "postgresql/PostgreSQL Tables.md",
     "postgresql/PostgreSQL Databases.md",
     "postgresql/Connect PostgreSQL on WSL 2 (Ubuntu).md",
     "postgresql/Install PostgreSQL on WSL 2 (Ubuntu).md",
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diff --git a/content/postgresql/PostgreSQL Insert and Import.md b/content/postgresql/PostgreSQL Insert and Import.md
@@ -1,6 +1,6 @@
 ---
 draft: false
-date: 2024-05-15 18:06
+date: 2024-05-16 00:50
 tags:
   - postgres
 ---
@@ -57,8 +57,6 @@ SELECT * FROM person
 # ...
 ```
 
-
-
 > [!info] References
 > - [Learn PostgreSQL Tutorial - Full Course for Beginners - YouTube](https://www.youtube.com/watch?v=qw--VYLpxG4)
 > - [Mockaroo - Random Data Generator and API Mocking Tool](https://www.mockaroo.com/)
diff --git a/content/postgresql/PostgreSQL Select.md b/content/postgresql/PostgreSQL Select.md
@@ -1,14 +1,13 @@
 ---
 draft: false
-date: 2024-05-15 19:32
+date: 2024-05-16 00:49
 tags:
   - postgres
 ---
 
-Use `ORDER BY` to sort the result by one or more columns.
+Use `ORDER BY` to sort the result by one or more columns. By default `ORDER BY` uses ascending order (`ASC`), you can change it to descending order by specifying `DESC`.
 
 ```sql
-# default is ASC
 SELECT * FROM person ORDER BY date_of_birth ASC;
 SELECT * FROM person ORDER BY date_of_birth DESC;
 SELECT * FROM person ORDER BY gender DESC, date_of_birth ASC;
@@ -17,37 +16,56 @@ SELECT * FROM person ORDER BY gender DESC, date_of_birth ASC;
 Use `DISTINCT` to list all distinct values in a column or a combination of columns.
 
 ```sql
-SELECT DISTINCT gender FROM person
-SELECT DISTINCT gender, last_name FROM person
+SELECT DISTINCT gender FROM person;
+SELECT DISTINCT gender, last_name FROM person;
 ```
 
-Use `WHERE` and 
+Use `WHERE` with or without the following keywords or operators to select rows with conditions. 
 
+- Use `AND`, `OR` to find union or intersection of conditions
+- Use comparison operators like `>`, `<`, `>=`, `<=`, `=`, `<>` 
+- Use `IN` to quickly select the matching ones in a pool
+- Use `BETWEEN AND` to select values between a range
+- Use `LIKE` to find values with a certain pattern (Both `%` and `_` denote placeholder)
+- Use `ILIKE` to get the effect of `LIKE` but without the case sensitivity
 
-: `AND` `OR` `COMPARISON OPERATORS` `>` `<` `>=` `<=` `=` `<>` `IN` `BETWEEN AND` `LIKE` `ILIKE`
-
-
-`LIMIT`:
-
-
-`OFFSET`:
-
-
-`GROUP BY`:
-
-
-`GROUP BY HAVING`:
+```sql
+SELECT * FROM person WHERE gender = 'Agender';
+SELECT * FROM person WHERE gender = 'Male' AND date_of_birth > '2024-01-01';
+SELECT * FROM person WHERE gender = 'Male' OR gender = 'Female';
+SELECT * FROM person WHERE gender IN ('Male', 'Female', 'Agender');
+SELECT * FROM person WHERE id BETWEEN 50 AND 55;
+SELECT * FROM person WHERE last_name LIKE '%han';
+SELECT * FROM person WHERE last_name ILIKE '____lan';
+```
 
+Use `LIMIT` to show a certain number of rows. Then use `OFFSET` to skip the first N rows. 
 
-AGGREGATE FUNCTIONS
+```sql
+SELECT * FROM person LIMIT 5 OFFSET 10;
+```
 
+Use `GROUP BY` to group rows with the same column value into summary rows. `GROUP BY` is often used with aggregate functions, such as `COUNT()`, `SUM()`, `AVG()`, `MIN()`, `MAX()`. In addition, you can use `GROUP BY HAVING` to add conditions.
 
-`AS`:
+```sql
+SELECT gender, COUNT(*) FROM person GROUP BY gender;
+SELECT gender, COUNT(*) FROM person GROUP BY gender HAVING COUNT(*) > 15;
+SELECT gender, AVG(age) FROM person GROUP BY gender;
+SELECT gender, MIN(age) FROM person GROUP BY gender;
+SELECT gender, MAX(age) FROM person GROUP BY gender;
+```
 
+Use `AS` to assign aliases to columns that appear in the result.
 
-`COALESCE`:
+```sql
+SELECT date_of_birth AS birthday FROM person;
+```
 
+Use `COALESCE` as a useful tool for handling NULL values.
 
+```sql
+SELECT COALESCE(email, 'Not provided') FROM person;
+```
 
 > [!info] References
 > - [Learn PostgreSQL Tutorial - Full Course for Beginners - YouTube](https://www.youtube.com/watch?v=qw--VYLpxG4)