docs: add postgres case sensitivity (#891)

* add postgres case sensitivity

* Update content/blog/postgres-case-sensitivity.md

Co-authored-by: Copilot <[email protected]>

---------

Co-authored-by: Copilot <[email protected]>

Author: adela-bytebase

content/blog/postgres-case-sensitivity.md

@@ -0,0 +1,113 @@
+---
+title: 'Postgres Case Sensitivity Explained'
+author: Adela
+updated_at: 2025/09/19 18:00
+feature_image: /content/blog/postgres-case-sensitivity/cover.webp
+tags: Explanation
+description: 'An engineering perspective to evaluate Postgres case sensitivity'
+---
+
+PostgreSQL's case sensitivity rules can surprise even experienced developers. Here's the concise, no-gotchas guide.
+
+## 1. Identifiers (table/column names)
+
+* **Unquoted identifiers are folded to lowercase.**
+
+  ```sql
+  CREATE TABLE Customer (ID int, UserName varchar(50));
+  -- Actually created as: customer(id, username)
+  
+  SELECT * FROM customer;   -- ✅ works
+  SELECT * FROM Customer;   -- ✅ works (folded to lowercase)
+  ```
+
+* **Quoted identifiers preserve case and must be referenced exactly.**
+
+  ```sql
+  CREATE TABLE "Customer" ("ID" int, "UserName" varchar(50));
+  
+  SELECT * FROM "Customer";           -- ✅ works
+  SELECT * FROM customer;             -- ❌ ERROR: relation "customer" does not exist
+  SELECT id FROM "Customer";          -- ❌ ERROR: column "id" does not exist
+  ```
+
+**Best practice:** avoid quoted identifiers. Use lowercase `snake_case` (e.g., `order_items`, `created_at`).
+
+## 2. Strings (data values)
+
+* **String comparisons are case-sensitive by default.**
+
+  ```sql
+  SELECT 'abc' = 'ABC';  -- false
+  INSERT INTO users (username) VALUES ('JohnDoe'), ('janedoe');
+  SELECT * FROM users WHERE username = 'johndoe';  -- 0 rows
+  ```
+
+* **Case-insensitive matching**
+
+  * Functions and operators:
+
+    ```sql
+    SELECT * FROM users WHERE lower(username) = 'johndoe';  -- ✅ finds 1 row
+    SELECT * FROM users WHERE username ILIKE 'john%';       -- ✅ case-insensitive LIKE
+    SELECT * FROM users WHERE username ~* '^john';          -- ✅ case-insensitive regex
+    ```
+
+  * `citext` extension:
+
+    ```sql
+    CREATE EXTENSION IF NOT EXISTS citext;
+    CREATE TABLE users (id SERIAL, username CITEXT UNIQUE);
+    SELECT * FROM users WHERE username = 'johndoe';  -- ✅ automatically case-insensitive
+    ```
+
+  * Nondeterministic collations (PostgreSQL 12+):
+
+    ```sql
+    CREATE COLLATION case_insensitive (
+        provider = icu, 
+        locale = 'und-u-ks-level2', 
+        deterministic = false
+    );
+    CREATE TABLE users (username TEXT COLLATE "case_insensitive");
+    ```
+
+## 3. Indexing for case-insensitive search
+
+* Functional index to avoid full scans:
+
+  ```sql
+  CREATE INDEX users_name_lower_idx ON users (lower(name));
+  -- Query must match the expression:
+  SELECT * FROM users WHERE lower(name) = lower($1);
+  ```
+
+* For prefix searches:
+
+  ```sql
+  CREATE INDEX users_name_lower_like_idx ON users (lower(name) text_pattern_ops);
+  SELECT * FROM users WHERE lower(name) LIKE lower($1) || '%';
+  ```
+
+## 4. ORMs & migrations: common pitfalls
+
+* Some ORMs emit **quoted identifiers**, locking you into exact casing everywhere. Prefer ORM settings that generate unquoted, lowercase names.
+* Mixing quoted and unquoted names across migrations leads to "why can't it find my table?" bugs — standardize on lowercase, unquoted schema objects.
+
+```sql
+-- Wrong: Mixing quoted and unquoted
+CREATE TABLE user_accounts (user_id SERIAL);
+ALTER TABLE "User_Accounts" ADD COLUMN email VARCHAR(100);  -- ❌ Fails
+
+-- Correct: Consistent unquoted
+ALTER TABLE user_accounts ADD COLUMN email VARCHAR(100);    -- ✅ Works
+```
+
+## Quick Rules of Thumb
+
+1. **Schema:** lowercase + unquoted identifiers, always.
+2. **Search:** use `ILIKE`, `lower()` with functional indexes, or `citext`.
+3. **Avoid quoted names** unless you have a compelling reason.
+4. **ORMs:** configure to generate lowercase, unquoted schema objects.
+
+That's it — you'll stay consistent, avoid case traps, and keep queries fast.