docs(ibm-db2): add and update notes

Author: lzwjava

Diff for: notes/2025-04-09-ibm-db2-add-column-en.md

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+---
+title: Adding a Column to an Existing Table in IBM Db2
+lang: en
+layout: post
+audio: false
+translated: false
+generated: true
+---
+
+To add a column to an existing table in IBM Db2, you use the `ALTER TABLE` statement with the `ADD COLUMN` clause. Here’s the basic syntax:
+
+```sql
+ALTER TABLE table_name
+ADD COLUMN column_name data_type [constraints];
+```
+
+### Example
+Suppose you have a table named `employees` and you want to add a column called `phone_number` with a data type of `VARCHAR(15)`:
+
+```sql
+ALTER TABLE employees
+ADD COLUMN phone_number VARCHAR(15);
+```
+
+### Key Points
+1. **Table Name**: Replace `table_name` with the name of your existing table.
+2. **Column Name**: Specify the new column name (e.g., `phone_number`).
+3. **Data Type**: Define the data type (e.g., `VARCHAR`, `INTEGER`, `DATE`, etc.).
+4. **Constraints (Optional)**: You can add constraints like `NOT NULL`, `DEFAULT`, or `CHECK` if needed. For example:
+   ```sql
+   ALTER TABLE employees
+   ADD COLUMN phone_number VARCHAR(15) NOT NULL DEFAULT 'N/A';
+   ```
+
+5. **Existing Data**: When you add a column, Db2 will populate it with `NULL` values for existing rows unless you specify a `DEFAULT` value.
+
+### Notes
+- You need appropriate permissions (e.g., `ALTER` privilege) on the table to perform this operation.
+- If the table is large, this operation might take some time and could lock the table, depending on the Db2 version and configuration.
+
+Let me know if you need help with a specific example or additional details!

Diff for: notes/2025-04-09-ibm-db2-describe-table-en.md

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-title: Using the DESCRIBE Command in IBM DB2
+title: Using the DESCRIBE Command in IBM Db2
 lang: en
 layout: post
 audio: false

Diff for: notes/2025-04-09-ibm-db2-sql-syntax-en.md

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-title: IBM DB2 SQL Syntax Exception
+title: IBM Db2 SQL Syntax Exception
 lang: en
 layout: post
 audio: false

Diff for: notes/2025-04-09-ibm-db2-table-sql-en.md

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-title: IBM DB2 Table SQL
+title: IBM Db2 Table SQL
 lang: en
 layout: post
 audio: false