docs(notes): add ibm-db2 column note

Author: lzwjava

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

@@ -38,4 +38,59 @@ ADD COLUMN phone_number VARCHAR(15);
 - 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!
+Let me know if you need help with a specific example or additional details!
+
+---
+
+The error you're encountering (`SQLCODE=-104, SQLSTATE=42601`) in IBM Db2 indicates a syntax issue with your `ALTER TABLE` statement. Specifically, `BIGINT(8)` is not a valid syntax in Db2. Unlike some other databases (e.g., MySQL), Db2 does not use a length or precision specifier like `(8)` with the `BIGINT` data type. In Db2, `BIGINT` is a fixed 8-byte integer type that can store values from `-2^63` to `2^63-1`, and you simply declare it as `BIGINT` without additional parameters.
+
+### Correct Syntax
+To add a `BIGINT` column with a `NOT NULL` constraint, use this:
+
+```sql
+ALTER TABLE table_name
+ADD COLUMN column_name BIGINT NOT NULL;
+```
+
+### Example
+If your table is called `employees` and you want to add a column `employee_id` as a `BIGINT` that cannot be null:
+
+```sql
+ALTER TABLE employees
+ADD COLUMN employee_id BIGINT NOT NULL;
+```
+
+### Why the Error Occurred
+- The `(8)` in `BIGINT(8)` is invalid in Db2 because `BIGINT` doesn't take a length argument. This syntax might be familiar from other databases like MySQL, where it specifies display width, but Db2 doesn't support it.
+- The parser encountered `BIGINT(8)` and flagged it as an "unexpected token," leading to the `SQLCODE=-104` error.
+
+### Fixing the Issue
+1. Remove the `(8)` from your statement.
+2. If you need to specify a default value (since `NOT NULL` requires existing rows to have a value), add a `DEFAULT` clause. For example:
+
+```sql
+ALTER TABLE employees
+ADD COLUMN employee_id BIGINT NOT NULL DEFAULT 0;
+```
+
+Without a `DEFAULT`, adding a `NOT NULL` column to a table with existing rows will fail because Db2 won't know what value to assign to the new column for those rows.
+
+### Steps to Resolve
+- If your table has no rows yet, simply use:
+  ```sql
+  ALTER TABLE table_name
+  ADD COLUMN column_name BIGINT NOT NULL;
+  ```
+- If your table already has rows, include a `DEFAULT` value:
+  ```sql
+  ALTER TABLE table_name
+  ADD COLUMN column_name BIGINT NOT NULL DEFAULT 0;
+  ```
+
+### Verification
+After running the statement, you can verify the column was added with:
+```sql
+DESCRIBE TABLE table_name;
+```
+
+Let me know if you still encounter issues or need further clarification!